Tales Imbiriba, Member, IEEE Ricardo Augusto Borsoi
email: raborsoi@gmail.com

Senior Member, IEEE José Carlos Moreira Bermudez

J C M Bermudez
email: j.bermudez@ieee.org.

C Richard
email: cedric.richard@unice.fr.

Deep Generative Models for Library Augmentation in Multiple Endmember Spectral Mixture Analysis

Keywords: Hyperspectral, endmember variability, spectral unmixing, generative models, MESMA, spectral libraries

Multiple Endmember Spectral Mixture Analysis (MESMA) is one of the leading approaches to perform spectral unmixing (SU) considering variability of the endmembers (EMs). It represents each EM in the image using libraries of spectral signatures acquired a priori. However, existing spectral libraries are often small and unable to properly capture the variability of each EM in practical scenes, which compromises the performance of MESMA. In this paper, we propose a library augmentation strategy to increase the diversity of existing spectral libraries, thus improving their ability to represent the materials in real images. First, we leverage the power of deep generative models to learn the statistical distribution of the EMs based on the spectral signatures available in the existing libraries. Afterwards, new samples can be drawn from the learned EM distributions and used to augment the spectral libraries, improving the overall quality of the SU process. Experimental results using synthetic and real data attest the superior performance of the proposed method even under library mismatch conditions.

I. INTRODUCTION

Spectral Unmixing (SU) aims at extracting the spectral signatures of materials present in the hyperspectral images (HI) of a scene, which are called endmembers (EMs), as well as the proportion to which they contribute to each HI pixel [START_REF] Keshava | Spectral unmixing[END_REF]. The SU problem can be solved using algorithms that are either supervised, where the EMs are known a priori, or unsupervised, where the EMs are estimated from the HI [START_REF] Ammanouil | Blind and fully constrained unmixing of hyperspectral images[END_REF]. The most popular model to describe the interaction between light and the targets is the Linear Mixing Model (LMM), which represents the reflectance at each pixel as a convex combination of the spectral signatures of the EMs [START_REF] Keshava | Spectral unmixing[END_REF]. However, the LMM fails to represent important nonideal effects observed in practice, such as nonlinear interactions between light and the materials [START_REF] Heylen | A review of nonlinear hyperspectral unmixing methods[END_REF]- [START_REF] Imbiriba | Band selection for nonlinear unmixing of hyperspectral images as a maximal clique problem[END_REF] and variations of the EM spectra along the scene [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF], [START_REF] Imbiriba | Generalized linear mixing model accounting for endmember variability[END_REF].

EM variability is an important effect originating from environmental, illumination or atmospheric changes which may lead to significant estimation errors in SU [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF]. The most prominent approach to deal with EM variability in SU consists in modeling EMs as sets of spectral signatures, also called spectral libraries [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF]. The spectral signatures in each library are variants of a material produced under different acquisition conditions or physico-chemical compositions. They are usually acquired a priori through laboratory or in situ measurements. The SU problem then becomes equivalent to selecting a subset of signatures in the libraries that can best represent the observed HI under the LMM. The methods that attempt to solve this problem can be roughly divided between sparse SU [START_REF] Iordache | Total variation spatial regularization for sparse hyperspectral unmixing[END_REF], [START_REF] Borsoi | A fast multiscale spatial regularization for sparse hyperspectral unmixing[END_REF] and Multiple Endmember Spectral Mixture Analysis (MESMA) [START_REF] Roberts | Mapping chaparral in the santa monica mountains using multiple endmember spectral mixture models[END_REF] algorithms. The MESMA algorithm is widely used due to its simplicity and interpretability, and has been widely employed in practice [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF]. However, the quality of the MESMA results is strongly dependent on how well the spectral libraries represent the EM signatures actually present in the scene. This is a problem since spectral libraries are usually not acquired under the same conditions as the observed HI, since in situ measurements can be costly or impractical. Furthermore, most existing spectral libraries only have very few signatures of each material, and might not adequately capture spectral variability occurring in the scene.

One approach to alleviate this problem consists of generating multiple synthetic samples of an endmember using a physical model (radiative transfer function -RTF) describing the variability of the spectra as a function of atmospheric or biophysical parameters [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF], such as e.g. the PROSPECT of Hapke models [START_REF] Jacquemoud | PROSPECT: A model of leaf optical properties spectra[END_REF], [START_REF] Hapke | Bidirectional reflectance spectroscopy, 1, Theory[END_REF] for vegetation or mineral spectra. These additional signatures are then included in the library to augment it before performing SU. The use of RTFs to generate spectral libraries has great potential since it can represent spectral variability caused by different effects which are unlike to be captured by laboratory or field measurements [START_REF] Peddle | Spectral mixture analysis and geometric-optical reflectance modeling of boreal forest biophysical structure[END_REF]- [START_REF] Somers | A conceptual framework for the simultaneous extraction of sub-pixel spatial extent and spectral characteristics of crops[END_REF]. However, physics-based models require accurate knowledge of the physical process governing the observation of the materials spectra by the sensor, which is hard to obtain in practice. This limits the practical interest of these methods.

Recently, deep generative models (DGMs) have seen remarkable advances in the form of variational autoencoders (VAEs) and generative adversarial networks (GANs) [START_REF] Kingma | Auto-encoding variational bayes[END_REF], [START_REF] Goodfellow | Generative adversarial nets[END_REF]. This have made it possible to learn the distribution of complex data (e.g., natural images) efficiently, and from a limited amount of samples [START_REF] Antoniou | Data augmentation generative adversarial networks[END_REF]. DGMs have been considered for data augmentation in few-sample settings for image classi-fication problems [START_REF] Antoniou | Data augmentation generative adversarial networks[END_REF]. A recent work proposed to use DGMs learned from observed HIs in order to parametrize the variable EM spectra in the optimization step of a matrix factorizationbased blind SU problem, where the EMs are estimated from the HI [START_REF] Borsoi | Deep generative endmember modeling: An application to unsupervised spectral unmixing[END_REF]. This showed that using generative neural networks is a promising approach to represent the EMs in SU.

In this paper, we propose a spectral library augmentation method for MESMA-based algorithms by leveraging the power of DGMs to represent the EMs. The main contribution of the proposed method is that it works blindly, what allows for augmentation of the spectral libraries used with MESMA even when RTFs or physical models are unknown. The overall strategy can be divided in three steps. First we learn the statistical distribution of each EM in the scene using the spectral signatures contained in the existing spectral library and a DGM. Then, we sample new spectral signatures using the DGMs and augment their respective spectral libraries. Finally, we unmix the observed HI using MESMA and the augmented library. Simulations with synthetic and real data show a substantial accuracy gain in abundance estimation when comparing the proposed method with competing strategies.

II. SPECTRAL UNMIXING WITH MESMA

Most MESMA algorithms consider the LMM as their central building block. The LMM assumes that each L-band pixel y n ∈ R L , n = 1, . . . , N , of a N -pixel HI, can be modeled as:

y n = M a n + e n , s. t. 1 a n = 1 and a n ≥ 0 (1)
where M ∈ R L×P is a matrix whose columns are the P EM spectral signatures m k , a n is the abundance vector and e n is an additive noise term. Differently from most LMM-based SU methodologies, which assume a unique EM for each material in the scene, MESMA considers multiple spectra libraries, or bundles, one for each endmember, and performs a search for the best fitting model within all possible combinations of endmembers. Thus, assuming prior knowledge of spectral bundles for each EM in the scene, the set M of endmember matrices that can be drawn from the library can be defined as

M = m 1 , . . . , m P : m k ∈ M k , k = 1, . . . , P (2)
where

M k = {m k,1 , . . . , m k,C k }, m k,j ∈ R L is a set of C k spectral signatures of the k th material. The MESMA SU problem can be formulated as min M ∈M, an y n -M a n 2 2 s. t. a n ≥ 0, 1 a n = 1. (3)
Although the MESMA algorithm has shown excellent performance when dealing with spectral variability in many practical scenarios, its performance is strongly effected by the quality of the spectral library M [START_REF] Somers | Endmember variability in spectral mixture analysis: A review[END_REF]. In order for MESMA to perform well, the library must be representative of the spectral library observed in a given scene. Previous works tried to address this issue by augmenting the spectral libraries using physics-based models that describe well the variability of the endmembers. See, e.g., the PROSPECT or Hapke models [START_REF] Jacquemoud | PROSPECT: A model of leaf optical properties spectra[END_REF], [START_REF] Hapke | Bidirectional reflectance spectroscopy, 1, Theory[END_REF]. However, a major drawback of physics-based models is the requirement of accurate knowledge of the physical process governing the observation of the materials spectra by the sensor. This detailed information is rarely available in practice, which limits the applicability of these methods. In the following, we will present a new approach for spectral library augmentation that is based on deep generative models such as VAEs and GANs. These approaches allows one to learn the statistical distribution of the endmembers from very few training samples, making it effective in practical scenarios.

III. LIBRARY AUGMENTATION WITH DGMS

Physics-based models describing the variations of the spectral signatures in a scene reveal an important characteristic of spectral variability: that EM spectra usually lies on a low-dimensional submanifold of the high-dimensional spectral space R L . This assumption is in agreement with most physical models, such as the PROSPECT or Hapke's [START_REF] Jacquemoud | PROSPECT: A model of leaf optical properties spectra[END_REF], [START_REF] Hapke | Bidirectional reflectance spectroscopy, 1, Theory[END_REF], which represent the spectral signature of the materials as a function of only a small number of photometric or chemical properties.

Instead of employing physics-based models, we propose in this paper to augment the spectral libraries by using deep generative models. Generative models aim to estimate the probability distribution p(X) of a random variable X ∈ R L based on a set of N x observations x i . Then, they allow one to generate new samples that look similar to new realizations of X. Such models have shown good performance at representing endmember spectra in blind unmixing applications [START_REF] Borsoi | Deep generative endmember modeling: An application to unsupervised spectral unmixing[END_REF].

Here we propose to use the signatures in existing spectral libraries to learn the generative models describing the distributions of EM spectra. Then, to enhance the ability of MESMA to adapt to a wider range of spectral variability, we augment the libraries by sampling from the estimated distributions. An illustrative outline of this strategy is shown in Fig. 1.

Even though the spectral dimensionality L is high compared to the small number of signatures often found in typical spectral libraries (making this problem very hard in general [START_REF] Neal | Annealed importance sampling[END_REF], [START_REF] Arjovsky | Wasserstein generative adversarial networks[END_REF]), the low-dimensinality of the manifolds to which the EM spectra is confined, allied with recent advances in generative models, have made this problem tractable. This framework has shown success in capturing the distribution of complex data such as natural images from very few training samples [START_REF] Antoniou | Data augmentation generative adversarial networks[END_REF], which illustrates its appropriateness for our application.

Deep generative models: A convenient way to estimate the PDF p(X) of a random variable X that lies on a lowdimensional submanifold of R L is to define a new random variable R K Z ∼ p(Z), with K L and a known distribution p(Z), and a parametric function (e.g. a neural network) G θ which maps Z → X ∈ R L such that the distribution of the transformed random variable X = G θ (Z) is very close to p(X). This allows us to generate new samples from X by first sampling from Z ∼ p(Z) and then applying the function G θ (Z). Although estimating G θ to fulfill this objective might seem difficult, recent advances in generative modeling such as VAEs [START_REF] Kingma | Auto-encoding variational bayes[END_REF] and GANs [START_REF] Goodfellow | Generative adversarial nets[END_REF] have shown excellent performance for modeling complex distributions (e.g., of natural images) using only a limited amount of samples [START_REF] Antoniou | Data augmentation generative adversarial networks[END_REF].

VAEs address this problem by maximizing a lower bound on the log-likelihood of p(X) [START_REF] Kingma | Auto-encoding variational bayes[END_REF]:

log p(X) ≥ E q φ (Z|X) log p(X|Z) -KL q φ (Z|X) p(Z) ,
where the function G θ is represented by p(X|Z), KL(• •) is the Kullback-Leibler divergence between two distributions, E ς {•} is the expected value operator with respect to the distribution ς and q φ (Z|X) is a variational approximation to the intractable posterior p(Z|X), which is also represented through another parametric function D φ : R L → R K .

Differently, GANs attempt to learn the distribution p(X) by seeking for the Nash equilibrium of a two-player adversarial game [START_REF] Goodfellow | Generative adversarial nets[END_REF] between the generator network G θ and a discriminator network C φ , which predicts the probability of a sample x i coming from the true distribution p(X) instead of being generated through G θ . The generator G θ is trained to maximize the probability of the discriminator making a mistake, which is formulated as the following minimax optimization problem:

min G θ max C φ E p(X) log C φ (X) + E p(Z) (1 -C φ (G θ (Z))) .
Although GANs are more flexible and have shown better results when modeling complex distributions, they are also much harder to train [START_REF] Arjovsky | Wasserstein generative adversarial networks[END_REF]. This motivated us to use VAEs in this work due their more stable training procedure. Future works will consider the use of GANs.

Library augmentation: Consider a small spectral library M known a priori containing a set of spectral signatures M i for each material i = 1, . . . , P . Each signature m i,j ∈ M i , j = 1, . . . , C k , can be viewed as a sample drawn from the statistical distribution of the i th EM spectra. Thus, these libraries can be employed as training data to learn a set of generative models G θi that represents the probability distribution function p i (M ) of each EM i = 1, . . . , P using a VAE [START_REF] Kingma | Auto-encoding variational bayes[END_REF].

Given the learned generative models G θi , we can then generate new spectral signatures from each EM class by sampling from the distribution of G θi (Z), where Z ∼ N (0, I K ). These new signatures can then be used to augment into the original library M, yielding a new spectral library M which is more comprehensive and better accounts for different spectral variations of each material. Finally, the MESMA algorithm can be applied to unmix each image pixel y n using the augmented library M. This procedure is described in detail in Algorithm 1, where the spectral library is augmented by adding N s samples to each EM set. Note that although this increases the complexity of SU with MESMA, approximate strategies can be used to obtain an efficient solution when the augmented library has many signatures [START_REF] Heylen | Hyperspectral unmixing with endmember variability via alternating angle minimization[END_REF]. Network architecture: To learn the generative models G θp , we used a VAE [START_REF] Kingma | Auto-encoding variational bayes[END_REF] due to its stable training [START_REF] Arjovsky | Wasserstein generative adversarial networks[END_REF] and because it behaved well with small spectral libraries. The architectures for G θp and D φp and the dimension of the latent spaces were selected as in [START_REF] Borsoi | Deep generative endmember modeling: An application to unsupervised spectral unmixing[END_REF] since they resulted in a good experimental performance and showed sufficient capacity to capture the spectral variability of a given library. The network architectures are shown in Table I and the latent spaces dimension was set to K = 2. Finally, the network training was performed with the Adam optimizer [START_REF] Kingma | Adam: A method for stochastic optimization[END_REF] in TensorFlow for 50 epochs.

IV. EXPERIMENTAL RESULTS

In this section, simulation results using both synthetic and real data illustrate the performance of the proposed method. We compare the performance of MESMA using the augmented library with that of the traditional MESMA algorithm. We also present results obtained with the fully constrained least squares (FCLS) and the the GLMM [START_REF] Imbiriba | Generalized linear mixing model accounting for endmember variability[END_REF], which estimate the endmembers from the observed HI (without using a spectral library). The VCA algorithm [START_REF] Nascimento | Vertex Component Analysis: A fast algorithm to unmix hyperspectral data[END_REF] was used to extract EMs used by the FCLS and GLMM methods. The performances were evaluated using the Root Mean Squared Error (RMSE) between the estimated abundance maps (RMSE A ) and between the reconstructed images (RMSE Y ). The RMSE between two matrices is defined as RMSE X = X -X * 2 F / N X , where N X denotes the number of elements in X.

Synthetic data with library mismatch: In this example, we evaluate the performance of the proposed approach quantitatively using a synthetic data set with three endmembers and L = 198 spectral bands. The goal is to simulate a typical library mismatch scenario often found when considering library-based unmixing [START_REF] Iordache | Total variation spatial regularization for sparse hyperspectral unmixing[END_REF]. To generate and process this dataset, we first obtained two disjoint sets of endmember spectra M 1 i and manually extracting pure pixels of soil, vegetation and water from a real hyperspectral scene (the Jasper Ridge HI [START_REF] Imbiriba | Low-rank tensor modeling for hyperspectral unmixing accounting for spectral variability[END_REF]).

M 2 i , with M 1 i ∩ M 2 i = ∅, i ∈ {1, 2, 3} by
The sets M 1 i contained 20 signatures each and were used to compose the synthetic pixel spectra y n , while each of the sets M 2 i contained 14 signatures that were employed to construct the spectral libraries used by MESMA to perform SU. We simulated a library mismatch by applying a random affine transformation (a gain and an additive scaling in the intervals [0.75, 1.25] and [-0.15, 0.15], respectively) to each element of M 1 i , i ∈ {1, 2, 3}. To generate each pixel, we used the LMM considering abundance fractions a n sampled from a Dirichlet distribution with concentration parameters selected such as to have a heavily mixed data in order to evaluate the methods in a challenging scenario, and pixel-dependent endmember matrices obtained by randomly (uniformly) selecting one spectral signature from each of the sets M 1 i , i ∈ {1, 2, 3}. White Gaussian noise with a signal to noise ratio (SNR) of 30dB was added to the data.

The final library M available for the MESMA-based methods was created by sampling five signatures at random of each material from M 2 i , and no other preprocessing or adequacy strategy was used to mitigate mismatch between the available library and the true endmembers used to construct the scene. Only the spectra in M was used to learn the DGMs, and N s = 3 additional signatures were sampled for each material. Finally, in order to provide a proper statistical evaluation, this whole procedure was repeated for 10 4 Monte Carlo realizations. The mean values and standard deviations are shown in Table II. It can be seen that despite only a small number of signatures being available to train the DGMs, the proposed strategy provided a substantial (16%) improvement in the abundance estimation RMSE when compared to the MESMA algorithm. This shows that with a careful selection of the neural network architecture, the proposed method can work even under such challenging conditions. When compared with the other methods the proposed solution improvement is even more significant obtaining gains of 70% (FCLS) and 67% (GLMM). These experiments show that the proposed data augmentation strategy can lead to significant performance gains when compared to the plain MESMA algorithm.

To investigate the influence of the parameter N s on the performance of the proposed method, we repeated this experiment for different values of N s ∈ {0, . . . , 8} and evaluated the behavior of RMSE A . The results, also seen in Table II, show that RMSE A decreases with N s . However, the performance improvements get small after about N s > 3, which indicates that a value of N s ≤ 3 can yield a good compromise between abundance estimation performance and computational complexity.

Real data: For the simulations with real data, we considered the Alunite Hill subscene of the Cuprite HI with 16×28 pixels, and a subscene of the Gulfport HI with 54×70 pixels [START_REF] Heylen | Hyperspectral unmixing with endmember variability via alternating angle minimization[END_REF]. Water absorption or low SNR bands were removed and both the images and the spectral libraries were rescaled to have the same number of bands, resulting in L = 181 for the Alunite Hill and L = 192 for Gulfport. These images were selected since the unmixing results can be evaluated using high-resolution classification maps available a priori, shown in Fig. 2. The libraries M were built by selecting two signatures of each endmember from the USGS library and from field surveys (for the Alunite Hill and Gulfport HIs, resp.) such that the MESMA results closely approached (visually) the ground truth. N s = 2 additional signatures per EM were generated.

The abundance maps reconstructed by all algorithms are provided in Figs. 3 and5. It can be seen that the abundance maps of the MESMA-based methods are significantly closer to the ground truth when compared to the GLMM and FCLS results. Furthermore, the proposed library augmentation strategy led to a much better representation of the alunite and kaolinite endmembers when compared to the competing approaches in the Alunite Hill HI. Similar results were obtained for the Gulfport HI, where the abundances obtained by the proposed method for the sidewalk and asphalt EMs approach the ground truth more closely when compared to those estimated by FCLS, GLMM and by MESMA with the original library. The spectral signatures generated using the DGMs, also seen in Figs. 3 and5, show that the proposed strategy is able to generate signatures that accommodate variability seen in typical scenes from its representation in the original library. Specifically, a generally agreeable shape but different scaling variations that act nonuniformly over the spectral space can be seen in all cases except for the ground/dirt EM in the Gulfport HI, whose original field surveyed spectra (contained in M) did not contain a meaningful amount of spectral variability.

The quantitative RMSE Y results in Table II show that the FCLS achieves smaller reconstruction errors in the real datasets when compared to the synthetic one, which contains more heavily mixed pixels and thus results in a worse data fitting for the FCLS (which is based on the VCA). However, we note that RMSE Y is not a good measure of unmixing performance, as an infinite number of combinations (endmembers, abundances) often leads to the same reconstructed HI.

To compare the proposed method with physics-based library augmentation, we considered a Lambertian scattering approximation of the Hapke model to augment the library used with the Alunite Hill HI. Given prior knowledge about the laboratory acquisition conditions of the spectra in the USGS library, we can generate different variations of these mineral spectra by considering different viewing geometries as detailed in [START_REF] Heylen | A review of nonlinear hyperspectral unmixing methods[END_REF]. The abundances estimated by MESMA using the augmented library are shown in Fig. 4. Although a clear improvement can be seen in the alunite and muscovite EMs when compared to the original library, the kaolinite abundances were completely absorbed into the muscovite abundance map. Moreover, the alunite region is smaller than what is indicated in the ground truth, which is more closely matched by the results obtained using the proposed method. This shows that the proposed strategy can be competitive with physics-based models in practice.

V. CONCLUSIONS

In this work, a novel spectral library augmentation strategy was proposed for MESMA-like algorithms. Using the spectral signatures present in existing libraries as training samples, we applied deep generative models to learn the statistical distribution of endmember spectra. This allowed us to sample new spectral signatures from the estimated endmember distribution, which were then included in the augmented library, improving its ability to properly represent the materials present in practical scenes. Simulation results with both synthetic and real data showed that the proposed methodology can significantly improve the performance of the MESMA algorithm.

Figure 1 .

 1 Figure 1. Outline of the proposed approach: deep generative models are used to approximate the distribution of spectra belonging to a library. Then, new spectral samples (right) can be obtained by propagating samples drawn from the EM submanifold through G θ and used to augment the spectral library.

Algorithm 1 : 5 M 8

 158 MESMA with spectral library augmentation Input : Y , M i , i = 1, . . . , P and Ns. 1 for i = 1, . . . , P do 2 Set M i = M i and train a DGM G θ i using the samples in M i ; 3 for j = 1, . . . , Ns do 4 Sample z ∼ N (0, I) and compute m = G θ i (z); Set M = [m 1 , . . . , m P ] : m k ∈ M i , i = 1, . . . , P ; 9 Run MESMA with the augmented library M to compute A ; 10 return A, M ;

Figure 2 .

 2 Figure 2. "Ground truth" for the Alunite Hill (left) and Gulfport (right) HIs.

Figure 3 .

 3 Figure 3. Left: abundance maps for the Alunite Hill subscene. Right: original endmembers (solid line) and synthetically generated signatures (dashed line).

Figure 4 .

 4 Figure 4. Abundance maps of MESMA for the Alunite Hill HI with a spectral library augmented using the Hapke model with known acquisition conditions.

Figure 5 .

 5 Figure 5. Left: abundance maps for the Gulfport subscene. Right: original endmembers (solid line) and synthetically generated signatures (dashed line).

Table I ENCODER

 I AND DECODER NETWORK ARCHITECTURES.

		Layer	Activation	Number of units
		Input	-	L
	D φ	Hidden # 1 Hidden # 2	ReLU ReLU	1.2 × L + 5 max L/4 , K + 2 + 3
		Hidden # 3	ReLU	max L/10 , K + 1
		Hidden # 1	ReLU	max L/10 , K + 1
	G θ	Hidden # 2 Hidden # 3	ReLU ReLU	max L/4 , K + 2 + 3 1.2 × L + 5
		Output	Sigmoid	L

Table II SIMULATIONS

 II WITH SYNTHETIC AND REAL DATA (VALUES ×10 3). ± 32.2 0.73 ± 0.87 0.47 ± 0.60 1.00 ± 2.06 GLMM 45.3 ± 31.2 0.30 ± 0.22 0.001 ± 0.002 0.002 ± 0.003 MESMA 18.2 ± 13.7 0.41 ± 0.45 19.2 ± 14.0 1.31 ± 2.02 Proposed 15.3 ± 11.0 0.26 ± 0.25 18.4 ± 12.8 1.16 ± 1.86 RMSE A of Algorithm 1 as a function of N s

		Synthetic HI		Alunite Hill	Gulfport
		RMSE A	RMSE Y		RMSE Y	RMSE Y
	FCLS 50.0 N s 0	1	2	3	4	5	6
	RMSE A	18.18 16.23 15.65 15.34 15.21 15.09 15.01

This work has been supported by the National Council for Scientific and Technological Development (CNPq) under grants 304250/2017-1, 409044/2018-0, 141271/2017-5 and 204991/2018-8, and by the Foundation for Research Support of the State of Rio Grande do Sul (FAPERGS) under grant 19/2551-0001844-4. R.A. Borsoi is with the Department of Electrical Engineering, Federal University of Santa Catarina (DEE-UFSC), Florianópolis, , Nice, France.


Mathieu Le Meur
email: m.lemeur@hotmail.fr

Mohammed Boussafir

Claude Le Milbeau

Mathieu Debure
email: mathieu.le_meur@bordeaux-inp.fr

Francis Claret

Jean-Charles Robinet

Catherine Lerouge

Le Meur Mathieu

Boussafir Mohammed

Milbeau Le

Debure Claude

Claret Francis Robinet Mathieu

Lerouge Jean-Charles

Catherine

Le Milbeau Claude

Debure Mathieu

Robinet Jean-Charles

& Lerouge

Organic Matter Oxidation of the Tégulines Clay formation, (Paris Basin, France): Spatial Heterogeneities

Keywords: Tégulines Clay formation, weathering profile, oxidation, Bulk organic characterization, Palynofacies, Molecular organic characterization

Samples of Albian Tégulines Clay outcropping near Brienne-le-Château in the eastern part of the Paris Basin were subjected to a geochemical characterization of organic matter (OM), combining OM bulk Rock-Eval analysis (RE), organic petrography and molecular analysis. In this study, the objective was to investigate the oxidation of natural organic matter in critical zone developed in early reduced marine clay formation. For that purpose, core samples from three boreholes crosscutting the Tégulines Clay formation down to the Greensands were selected. Several meters of Brienne marls preserved Tégulines Clay from atmosphere and therefore from high weathering and high oxidation in AUB240 borehole, whereas Tégulines Clay were weathered in their upper part in AUB1010 and in AUB230 boreholes as a result to their vicinity to the surface. The results showed that the Total Organic Carbon (TOC) contents in all clays are very low, ranging between 0.3 and 0.7 wt.%. The RE bulk data and Tmax parameter of OM in preserved Tégulines Clay indicate that the OM is immature. The organic petrography shows a predominance of gel-like amorphous OM preserved by natural sulphurisation in anoxic environments. Organic matter in Tégulines Clay from the AUB230 and AUB1010 boreholes show similar characteristics. The OM at the top of Tégulines Clay contains large amounts of oxidized lignocellulosic debris and has high RE Oxygen-Index values. In the first upper 10 m of the clays, the RE bulk, organic petrography and molecular data revealed oxidative events (high OI and high oxidized debris contents). Below 10 m, the OM is almost preserved. The OM in the reduced marine Tégulines Clay formation is very little functionalized and seems to be slightly reactive but not negligibly with the inorganic fractions in presence of oxygen.

Introduction

Clay-rich geological formations are considered by many countries as natural barriers for radioactive waste isolation due to their low permeability and their sorption properties preventing the release of radioactive substances towards the biosphere. Most of previous investigations concerning clay-rich formations focus on deep systems (> 100 m) without direct interface with biosphere-atmosphere [START_REF] Hendry | Chloride and chlorine isotopes (36Cl and δ37Cl) as tracers of solute migration in a thick, clay-rich aquitard system[END_REF][START_REF] Hautevelle | Tracing of variabilities within a geological barrier by molecular organic geochemistry. Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)[END_REF][START_REF] Altmann | Diffusiondriven transport in clayrock formations[END_REF]). In the context of sub-surface waste repository, the vicinity of the surface can affect the solid-fluid equilibrium system of the geological formation due to weathering and oxidation phenomena involving in turn potential effects on solute transport properties with depth. Such phenomena in clay-rich formations are scarce and have been recently evidenced in the Lower Cretaceous Tégulines marine-clay formation (Tégulines Clay) near Brienne-Le-Chateau (Aube department, France) investigated for a decade in the context of sub-surface repository for low-level radioactive waste [START_REF] Debure | Influence of soil redox state on mercury sorption and reduction capacity[END_REF][START_REF] Debure | Retention of arsenic, chromium and boron on an outcropping clay-rich rock formation (the Tégulines Clay, eastern France)[END_REF][START_REF] Duffy | Designing a suite of models to explore critical zone function[END_REF][START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF][START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]. Like most of the marine clay-rich formations, Tégulines Clay evolved under reduced geochemical conditions during early diagenesis and its burial [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]). In the studied area, weathering and oxidation phenomena including changes of mineralogy, chemistry, and petrophysical properties occur in Tégulines Clay at vicinity of the surface, due to interactions with oxygen and meteoric waters. A gradual oxidation profile developed in the clay formation and the resulting effects on pore water chemistry were evidenced based on several indicators as sulfur and iron oxidation states [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF] and the changes of CO2 partial pressure [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF].

Reactivity of Organic Matter (OM) with oxygen is suspected to play a role on CO2 and redox regulation of the Tégulines Clay at vicinity of the surface.

In this study, we propose to investigate the reactivity of natural OM in Tégulines Clay as a marker of weathering and oxidation, using bulk and molecular techniques in the objective to better evaluate how atmosphere interacts with the rock and regulates its solid-fluid systems with depth. Organic Matter (OM) bulk analysis is firstly achieved by Rock-Eval analyses associated with palynofacies. This analytical approach allows determining the OM composition and its quality in term of maturity, refractory and redox state. Additional molecular organic geochemistry secondly completes the OM characterization, in term of origins (marine/terrestrial), maturity (saturated hydrocarbons) and oxidation (deposition mode J o u r n a l P r e -p r o o f and weathering). Such type of approach was previously applied in deep clay-rich geological formation [START_REF] Deniau | Comparison of the bulk geochemical features and thermal reactivity of kerogens from Mol (Boom Clay), Bure (Callovo-Oxfordian argillite) and Tournemire (Toarcian shales) underground research laboratories[END_REF][START_REF] Elie | Natural and laboratory oxidation of low-organic-carbon-content sediments: comparison of chemical changes in hydrocarbons[END_REF][START_REF] J O U R N A L P R E -P R O O F Elie | Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland[END_REF][START_REF] Hautevelle | Tracing of variabilities within a geological barrier by molecular organic geochemistry. Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)[END_REF][START_REF] Landais | Behavior of oxidized type II kerogen during artificial maturation[END_REF][START_REF] Landais | Utilisation de la géochimie organique pour la détermination du paléoenvironnement et de la paléothermicité dans le Callovo-Oxfordien du site de l'Est de la France[END_REF] and is here challenged in a sub-surface context.

Materials and methods

Geological setting and mineralogy

The studied area is located near Brienne-le-Chateau in the eastern part of the Paris Basin (Aube department, Figure 1 (a,b)). The Gault clay formation (Gault Clay) consists of siliciclastic shales deposited in an open marine environment from Middle to Upper Albian (Lower Cretaceous) on the Greensands formation (Amedro et al., 2014). The stratotype of the Gault Clay defined in the Aube department consists of Tégulines Clay (82 m) overlaid by the Brienne marls (43 m). At the maximum burial of the Paris Basin, temperatures reached 30-36°C in the Gault Clay [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]. In Early Miocene, the Paris Basin chalk formations were eroded. Nowadays the Gault Clay outcrops as an 8-10 km wide and 80-km long band of terranes-oriented NE-SW through the Aube department. The Brienne marls only subsist in the western part of the studied area, elsewhere the Tégulines Clay outcrops.

Its thickness increases from east to west between 60 and 120 m. Locally few meters of Quaternary surficial formations overly Gault Clay.

The unweathered Tégulines Clay essentially consists of clay minerals (47-72 %) associated with quartzfeldspar (28-43 %), carbonates (0-22%), and minor pyrite and phosphate nodules. Mineral variability in unweathered Tégulines Clay is mainly vertical (Fig. 1 (c)). The first 9-12 meters at the bottom of the clay formation is characterized as a clay-quartz rich unit (named UAQ), with the highest quartzfeldspar silty content (46 %) and the lowest carbonate content (3.5 %). The next 35-40 m constitutes a clay-rich unit (named UA) with a clay average content of 51 %, and intermediate carbonate and quartzfeldspar silty contents. The last 20-25 meters at the top of the clay formation constitutes a carbonateclay rich unit (named UAC), characterized by the highest carbonate content (9-25 %) and the lowest quartzfeldspar silty content (30 %). The UAC unit constitutes a transitory term with the Brienne marls [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF].

J o u r n a l P r e -p r o o f

Materials, sampling campaigns

Fifty-three core samples of Tégulines Clay were selected among three boreholes for the study of organic matter: 7 from the AUB240 borehole (2018 drilling campaign), 31 from the AUB230 borehole (2017 drilling campaign) and 15 from the AUB1010 borehole (2015 drilling campaign). Additional samples of soil and Quaternary surficial formations were collected in a trench (TPH 1-1) corresponding to the first meters of the AUB230 borehole, due to the difficulty to recover the first meters during the drilling.

In the AUB240 borehole, surficial formations and ~12 meters of Brienne marls overlaid the Tégulines Clay, allowing a protection for the Tégulines Clay. Consequently, core samples collected in the Tégulines horizon from this borehole can be considered as the most representative of compacted pristine Tégulines Clay. The AUB230 borehole, located on a ridge top in cropland, crosscut ~ 30 cm of brown soil, ~ 5 m of surficial formations (sandy loam) and ~ 63 m of Tégulines Clay down to Greensands. The AUB1010, located down the valley, crosscut less than 2 m of surficial formations and ~ 33 m of Tégulines Clay down to Greensands (Fig. 3).

Major mineralogy of the Tégulines Clay core samples from the AUB230 and AUB1010 deduced from XRD data treatment are consistent [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF][START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]

(fig. 1 (c)).
At the top of Tégulines Clay from the AUB230 and AUB1010 boreholes, claystone is sticky and grey with iron oxi-hydroxides. Interactions between Tégulines Clay and surficial oxidizing waters induce mineralogical changes such as pyrite oxidation, calcite dissolution and precipitation of iron hydroxides and gypsum between the top of the formation down to ~11 m. Detailed mineralogical, geochemical and petrophysical work on Tégulines Clay of the AUB1010 and AUB230 boreholes rather indicated an extension of the oxidation front down to ~20 m depth [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF][START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]. Current investigations provide evidence of ancient root network development down to ~12 m depth at least.

Methodology

Rock-Eval analysis (RE)

The type, quality and amount of OM preserved in TCF samples before and after thermal maturation were determined using new Rock-Eval 6® pyrolysis (Vinci Technologies, Rueil Malmaison). About 50 to 60 mg of powdered and dried samples were used for the analysis depending on the estimated OM J o u r n a l P r e -p r o o f contents. The pyrolysis program involved an isothermal stage at 200 °C, held 2 min under inert gas (helium); the temperature was then raised to 650 °C (30 °C.min-1) and held for 3 min. The oxidation phase started with an isothermal stage at 400 °C under purified air. Then, the oven temperature was raised to 750 °C (at 30 °C.min-1) and held for 5 min. New Rock-Eval 6® classical parameters and their significance were explained by Espitalie et al. (1985a,b) and [START_REF] Lafargue | Rock-Eval 6 applications in hydrocarbon exploration, production and soil contamination studies[END_REF]. 4 parameters were used in the present study: (i) the total organic carbon content (TOC, wt %), which accounts for the quantity of OM calculated from the integration of the amount of thermo-evaporated free hydrocarbons (S1 peak), hydrocarbons produced by kerogen pyrolysis (S2), S3CO and S3CO2 produced by the breakdown of kerogen under inert gas and S4CO and S4CO2 produced by the oxidation and the pyrolysis of residual carbon under purified air; (ii) the oxygen index (OI, mg CO2.g-1 TOC), which is the oxygenated quality of OM calculated from the S3 peak; (iii) the hydrogen index (HI, mg HC.g-1 TOC), which represents the amount of HC quality produced during pyrolysis (calculated from the S2 peak); (iv) the Tmax, which is deduced from the Tpic of Rock-Eval VI. Tpic is the temperature of the peak oil production during pyrolysis. Tmax is often used as an OM maturity indicator (Espitalie et al., 1985a,b). The Total Organic Carbon (TOC), the Hydrogen Index (HI) and the Oxygen Index (OI) are the 3 main parameters used in environmental science [START_REF] Di-Giovanni | Sur la présence de matière organique méso-cénozoïque dans les humus actuels (bassin de Chaillexon, Doubs, France)[END_REF][START_REF] Boussafir | Petrographical and geochemical study of modern lacustrine sedimentary organic matter J o u r n a l P r e -p r o o f (Lagoa do Caçò, Maranão, Brazil): Relationship between early diagenesis, organic sedimentation and lacustrine filling[END_REF].

Tpeak deduced from S2 spectra is also used in environmental science. It is the temperature of the oven for the maximum hydrocarbon released.

Thanks to the deconvolution of the S2 pyrolysis spectra using Peakfit software (SPSS®), we were able to show the presence of 5 elemental Gaussian distributions describing the release of the different pyrolytic molecular families at Tpeak temperatures (+-20°C) of 260 °C, 310 °C, 370 °C, 460 °C and 560 °C. The relative contribution of these different pyrolytic molecular compounds to the signal was also semi-quantified by the calculation of peak surfaces of the corresponding Gaussians plotted to those of the entire S2 signal surface.

Microscopic investigations

Initially developed by [START_REF] Combaz | Les palynofaciès[END_REF], the quantitative organic petrography is a method that consists to study thin slides under a microscope that permit the identification and the quantification of the organic J o u r n a l P r e -p r o o f compounds present in a constant amount of sediments (1 cm 3 or 1 gram) after the elimination of carbonate and silicate by hydrochloric and hydrofluoric treatments [START_REF] Graz | Quantitative palynofacies analysis as a new tool to study transfers of fossil organic matter in recent terrestrial environments[END_REF]. Optical investigations were performed with a DMR XP Leica microscope by using the transmitted light mode.

The approach is based on the distinction of different categories of petrographic components characterized by their optical, form properties and, origins [START_REF] Combaz | Les kérogènes vus au microscope[END_REF][START_REF] Tyson | Sedimentary organic matter: organic facies and palynofacies[END_REF]. This quantification was carried out on a minimum of 500 particles with a 50x magnification objective [START_REF] Di-Giovanni | Sur la présence de matière organique méso-cénozoïque dans les humus actuels (bassin de Chaillexon, Doubs, France)[END_REF], Sebag et al. 2006a,b, Graz et al. 2010). To achieve absolute quantification of palynofacies, a pollen standard of precise concentration has been introduced in the samples. [START_REF] Battarbee | The use of electronically counted microspheres in absolute diatom analysis[END_REF][START_REF] Vernal | Evaluation of palynomorph concentrations: do the aliquot and the marker-grain methods yield comparable results?[END_REF] In this study, the standard chosen is Cupressus sp. Because of its strong reaction under UV excitation thus eliminating any confusion. Three main classes were distinguished in the different samples: the amorphous organic matter, without any biological apparent structures, lignocellulosic debris inherited from higher plant and other particles distinguished by their easily recognizable morphology. Different categories were observed in these three main classes and are detailed in Table 1 andFigure 2.

Lipid molecular analysis

Lipids were extracted from ca. 5 g of dried sediment using a Dionex ASE 200 with a dichloromethane (DCM): methanol (MeOH) mixture (9:1 v/v; at 100 °C and 1000 psi for 5 min in 3 cycles). After solvent evaporation, the total extract was then separated into neutral, acid and polar fractions using liquid chromatography with aminopropyl bonded silica as solid phase [START_REF] Jacob | Pentacyclictriterpenemethylethers in recentlacustrinesediments (Lake Caço, Brazil)[END_REF]. 5α(H)-cholestane was added as an internal standard to the neutral and acid fractions and dried under N2 flux. The acid fraction samples were then methylated by adding a mixture of anhydrous MeOH and acetyl chloride kept at 60 °C for 1 h. The obtained methyl ester and neutral fractions were then derivatized by reacting 40 µl N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) in 60 µl pyridine at 60 °C for 1 h. and analyzed by GC-MS. GC-MS analyses were performed on a Trace GC coupled to a TSQ Quantum XLS mass spectrometer (both from Thermo Scientific). Gas chromatograph (GC) was fitted with a Trace Gold TG-5MS capillary column (60 m x 0.25 mm id, 0.25 µm film thickness). The sample was dissolved in toluene and injected J o u r n a l P r e -p r o o f with a splitless mode in a 2 µl volume. The injector temperature set at 280 °C. Helium was the carrier gas at a flow rate of 1 ml.min -1 . The GC operating conditions were as follows: temperature increase from 40 to 120 °C at 30 °C/ min and 120 to 310 °C at 3 °C/min with a final isothermal hold at 310 °C for 68 min. The mass spectrometer was operated in the electron ionization (EI) mode at 70 eV and scanned from 50 to 650 Daltons. The identifications of the different peaks were based on a comparison of mass spectra with published data. Lipids concentration was estimated by the comparison of TIC area of each lipid with that of the internal standard and normalized to the weight of the extracted sample.

Results and discussion

3.1 Rock Eval data 3.1.1 Quantitative and qualitative characterization of the OM For all the analyzed samples, the results obtained by Rock-Eval analysis are presented in Figure 3 and Supplementary data 1. While, the TOC values indicates an organic content below 1 wt.% for the Tégulines Clay, the content is varying with the depth with an increase from 0.36 to 0.59 wt.% in the first 10 meters and with a small variation around a 0.53 mean value in the deeper part. The Hydrogen Index (HI) and the Oxygen Index (OI) were reported both in the Figure 3 as a function of depth and in a Pseudo van Krevelen diagram to characterize the OM type (Fig. 4). Again, as detailed hereafter the first 10 m show a different behavior with a decrease of HI and OI while below 10 m OI and HI are homogeneous and showed almost no variation with depth

Soil and Quaternary formation

Soil and Quaternary formation are available only for AUB230. The soil at the top of the AUB230 borehole (TPH1-1 0-30 cm) has a TOC of 1.45 wt.%, and is characterized by high HI and OI values, revealing oxygenated immature OM. These data are in good agreement with soil data of the literature [START_REF] Copard | Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering[END_REF].

Quaternary surficial formation at the top of the Tégulines Clay in the AUB230 borehole does not contain any analyzable OM, except the samples at 4 and 5 m, that corresponds to the transition with Tégulines

J o u r n a l P r e -p r o o f

Clay. The latter show low but valid TOC, and a hydrogenated quality (HI) and oxygenated (OI) average ranging respectively between 100 and 286 mg HC. g -1 TOC and 268 and 307 mg CO2. g -1 TOC.

Tégulines Clay

Tégulines Clay in the AUB240 borehole (Fig. 3) shows homogenous RE parameters (TOC, HI, OI) suggesting stable OM and can be considered as a reference in term of types and preservation of OM in the clay formation for this study. TOC values are extremely low, ranging between 0.4 and 0.7 wt.%. The HI through the clay formation varies between 17 mg HC. g -1 TOC and 30 mg HC. g -1 TOC. The OI is ranging between 122 and 176 mg CO2.g -1 TOC.

TOC values of Tégulines Clay in the AUB230 borehole (AUB230 6.10 -68.45 m) range between 0.4and 0.7 % and are almost similar to that of Tégulines Clay in borehole AUB240. At the top of the clay formation at 6.00-6.10 m, TOC value of 0.4 is low compared to the soil (TPH1-1 0-30) and remains almost homogeneous until 45 m. In the deepest part (>45 m), the TOC increases slightly to reach 0.8 wt. %. At 70 m toward the transition with Greensands, the TOC decreases to 0.5 wt.% (Supplementary data 1). The HI decreases between 6 and 9 m (98 -25 mg HC. g -1 TOC) and remains stable, until 55 m where the HI increases again to reach 118 mg HC g -1 TOC at 68 m. The OI is relatively high (mean around 180 mg O2 g -1 TOC) between 6 and 9 m and remains stable until the depth of 45.84 m (around a mean of 76 mg O2 g -1 TOC). However, one pulse of OI can be observed at 21.3 m (117 mg CO2 g -1 TOC). Below 45.84 m the OI values decrease (37 to 48 mg O2 g -1 TOC). The RE parameters measured in Tégulines Clay of the AUB230 borehole allow discriminating three main parts corresponding to the top (6 -9 m), the center (10 -45 m) and the bottom of the borehole (55 -68 m). At the top of Tégulines Clay, the HI/OI relationship is quite classical with an obvious anti-correlation: the HI decreases and OI increases in this section demonstrating a classical oxidation profile [START_REF] J O U R N A L P R E -P R O O F Marchand | Organic carbon sources and transformations in mangrove sediments: a Rock-Eval pyrolysis approach[END_REF].

Tégulines Clay of the AUB1010 borehole (Fig. 3) are characterized by low TOC content at the surface and then remains homogenous with values comprised between 0.3 % and 0.6 %. The HI is high at the top (192 mg HC. g -1 TOC) and decreases rapidly at 3.31 m (81 mg HC. g -1 TOC). Deeper, the HI remains homogenous (17 -29 mg HC g -1 TOC). The HI value at 1.88 m is high (192 mg HC. g -1 TOC) as for the soil sample (TPH1-1 0-30) revealing more immature well-preserved OM. The OI values are J o u r n a l P r e -p r o o f extremely high at the surface (883 mg CO2.g -1 TOC and 912 mg CO2.g -1 TOC at 1.88 m and 3.31 m respectively) due to low TOC content and probably the input of surficial pedogenetic OM. Deeper, the OI decreases rapidly and remains relatively stable along with the profile (122 -241 mg CO2.g -1 TOC).

The trends of the HI/OI ratios in Tégulines Clay of the AUB1010 and the AUB230 boreholes are similar.

Tégulines Clay OM of the three boreholes plot in type III OM field, revealing the terrestrial origin and/or well-oxidized type II OM. Tégulines Clay OM of the borehole AUB240 shows intermediate OI and HI values indicating the most preserved conditions of OM. Tégulines Clay OM of the AUB230 borehole is a mixture of type II-and type III-OM, revealing 1) either the ratio of inherited marine OM (type II) and terrestrial input (type III) or 2) a degradation process of marine OM allowing a shift from type II-OM to an intermediate type with a decrease in the HI and a slight increase in the OI compared to the original quality of the OM at the time of its deposition. Tégulines Clay of borehole AUB1010 shows oxygenated OM revealing more oxic conditions resulting in a shift from type II or more terrestrial oxidized (Fig. 4).

Tmax and shape of the pyrolysis S2 peak

The S2 signal delivered by the Rock-Eval pyrolysis is a spectrum that allows defining the rate of pyrolysate hydrocarbons expressed as a function of temperature [START_REF] Copard | Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering[END_REF]. Deconvoluting the S2 signal permits us to better understand the evolution of the pyrolysis Temperature (Tpeak) to unravel the composition of the natural organic matter, which is generally composed of a complex mixture of organic compounds. The S2 peak is non-Gaussian and is accompanied by shoulders for the immature samples. The different peaks and shoulders correspond to the cracking of the different organic compounds [START_REF] Disnar | Etude expérimentale de la fixation de divers métaux sur une matière organique sédimentaire d'origine algaire. Maturation thermique des composés formés[END_REF]Disnard & Trichet 1984;[START_REF] Disnar | Soil organic matter (SOM) characterization by Rock-Eval pyrolysis : scope and limitations[END_REF]. The literature concerning the shape of the pyrolysis S2 peak is mainly focused on soils samples. In this study, the different peaks of OM in the soil sample (TPH1-1 0-30 cm) can be attributed to specific compounds. The S2 peak shows a broad shape and two Tpeak at 370 °C and 460 °C (C3 and C4) (Fig. 5a), typical of a soil sample and in agreement with the bulk RE results. The cluster C3, at 370 °C can be attributed to the thermal breakdown of biological constituents such as polysaccharides and lignin [START_REF] Disnar | Soil organic matter (SOM) characterization by Rock-Eval pyrolysis : scope and limitations[END_REF]). The C4 cluster shows more preserved OM. For this sample, cluster C1 is absent. In their study, [START_REF] Copard | Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering[END_REF] showed J o u r n a l P r e -p r o o f that the C1 cluster (260 °C) is more labile and easily mineralized and could be easily absent in the most diagenetically or pedogenetically evolved samples.

For OM in Tégulines Clay, the shape of the pyrolysis S2 peak does not permit to attribute a specific compound but will permit to interpret the results in term of preservation. The mathematical deconvolution of S2 peak show five molecular RE pyrolytic families named C1 to C5 with 260, 310, 370, 460 and 560 °C Tpeak respectively (Fig. 5, 6 and supplementary data 2).

Tégulines Clay OM in AUB240 borehole shows very homogeneous cluster contribution with depth (Fig. 5b; Fig. 6a). C4 is the major cluster encountered (80 %), followed by C3 and C5. The distribution of these contributions reveals preserved conditions with diagenetically well stabilized OM and are in accordance with the bulk RE values [START_REF] Copard | Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering[END_REF].

Tégulines Clay OM in AUB230 and AUB1010 boreholes show variations of the cluster distribution with depth. In AUB230 borehole, OM between 9 and 55 m show a high contribution of the C4 cluster (Fig. 5d, Fig. 6b supplementary data 2) that is almost similar to Tégulines Clay OM in AUB240 borehole,, revealing stable OM input in probably good preserved conditions. At 21 m, the C2 cluster is more represented indicating the presence of labile OM. At the top of the clay formation (6.10 m), OM is particular with a high contribution of the C1 cluster (Fig. 5c). This could be due to the presence of light recycled OM composed of a small molecular structure easily thermopyrolysable. At the bottom of the clay formation (67 and 68 m) (Fig. 5e), the higher contribution changes to C3 cluster also revealing stable and preserved OM [START_REF] Copard | Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering[END_REF].

Tégulines Clay OM in AUB1010 borehole (Fig. 5; Fig. 6c) shows an S2 deconvolution similar to that in AUB230 borehole. The most upper sample (AUB1010 1.88, Fig. 5f) is characterized by the contribution of C1, C3 and C4 (35, 45 and 20% respectively) clusters. The C1 cluster reveals the presence of thermally labile biological compounds and shows more immature OM that could be, as for the AUB230 6.10 m, a similar light recycled OM. Between 3 and 16 m, the major cluster is C4 (Fig. 5g,h): stable OM with a variable contribution of the other clusters. Between 17 and 34 m (Fig. 5i), the major cluster is C4, followed by C3 and C5. These conditions are similar to the AUB240 borehole and suggest more stabilized and preserved OM.

J o u r n a l P r e -p r o o f

The R400 parameter (proportion of the S2 peak integrated before 400°C, [START_REF] Disnar | Soil organic matter (SOM) characterization by Rock-Eval pyrolysis : scope and limitations[END_REF]) and depending on the proportion of labile and probably more diagenetically reactive biomolecules was also calculated (supplementary data 1). This parameter varied between 0.1 and 0.6 and was higher for surface samples (0.6 at 0-30 cm) indicating the presence of 60 % of labile OM in the surface. This parameter was low in the AUB240 borehole (0.10 -0.14) which is related to the 90 % of more stable OM (10 % of labile OM) with highly refractory character.

Tmax is also largely used in the literature in order to characterize the maturity of the OM. A general overview of the samples reveal that the Tmax is lower than 430 °C, suggesting that the OM is considered immature.

Quantitative palynofacies investigations

The particles observed in the different samples were identified following the different morphological and textural criteria presented in Fig. 2 and table 1. All the acronyms cited in the next section are detailed in the table 1.

The quantitative palynofacies results for TPH1-1 are presented in Fig. 7a. As expected from the Rock-Eval results, the sample collected in the first 30 cm (0-30 cm) reveals a predominance of preserved lignocellulosic fragments (plc), slightly degraded lignocellulosic fragments (slc) plc+slc (4.41 mg. g -1 ) and divers particles (div) (1.70 mg.g -1 ). The pyrite is absent at this depth. These lignocellulosic compounds are, in their majority under gel-like forms, suggesting the sequestration of these particles in an anoxic hydromorphic environment permitting protection artificially the OM [START_REF] Boussafir | Petrographical and geochemical study of modern lacustrine sedimentary organic matter J o u r n a l P r e -p r o o f (Lagoa do Caçò, Maranão, Brazil): Relationship between early diagenesis, organic sedimentation and lacustrine filling[END_REF].

These parameters are in accordance with the RE data (high TOC, HI) and S2 deconvolution are typical of a soil sample. The samples from the trench collected below 30 cm (30 cm to 5 m) did not permit to perform any quantitative analysis due to the too-small number of residual particles in the palynofacies.

Tégulines Clay OM in AUB240 borehole (Fig. 7b) shows a homogeneous palynofacies content with depth. The major particles encountered are the grAOM (1.11 -2.31 mg.g -1 ) followed by the OgAOM (0.06 -0.69 mg.g -1 ) and do (0.26 -0.51 mg.g -1 ). OgAOM content increases between 29 and 80 m (0.06 mg.g -1 -0.69 mg.g -1 ) and pyrite is observed in inclusion. All these features suggest preserved anoxic conditions of the initial deposit and agree with the RE and deconvolution results.

J o u r n a l P r e -p r o o f

For the borehole AUB230 (Fig. 7c), at 6.10 m, the palynofacies is dominated by grAOM (1.03 mg.g -1 ).

There is also the presence of pyrite (0.59 mg.g -1 ) and od (0.27 mg.g -1 ) with small particles (between 10 and 20 µm). In addition, the div category decreases in comparison with the surface. At 9.36 m, the palynofacies is characterized by small particles (around 1 µm) and pyrite is absent. The presence of small black particles as opaque-debris and/or oxidized Lignocellulosic particles suggests more oxidative conditions. Between 10 and 18 m the grAOM is present in a higher proportion (between 1.47 and 4.51 mg.g -1 ). The proportion of OgAOM is higher than the 9.36 m sample (between 0.090 and 0.24 mg.g -1 ).

The od proportion is homogeneous in this depth range. At 25 m, the proportion of OgAOM increases (0.35 mg.g -1 ) and the pyrite content also increases (0.49 mg.g -1 ). Between 30 and 55 m, the proportion of grAOM is higher than the other samples (between 1.99 and 4.83 mg.g -1 ) there is also the presence of pyrite and the od category detains bigger size (~100 µm). At the end of the borehole, (55-68 m), the proportion of grAOM is the highest (4.83-6.83 mg.g -1 ), the OgAOM proportion is also high (0.57-0.84 mg.g -1 ) with bigger size and pyrite in inclusion. The palynofacies show a higher contribution of grAOM and OgAOM with pyrite inclusion. This feature also shows more preserved conditions. The increase of the AOM particles is correlated with the increase of HI and the principal contribution of C3 cluster suggesting that this AOM is the principal component of kerogen and suggest more preserved conditions of the formation.

The palynofacies for the AUB1010 borehole was difficult to interpret because the particles were present in very low proportion and could not permit any quantitative work. The particles were mainly composed of very small (around 1 µm) OgAOM and od particles. The samples of the AUB1010 borehole are similar to the AUB230 (6.10 m) sample and suggest more oxidative conditions.

The palynofacies is representative of the organic matter composition after the sedimentation and the organic diagenesis [START_REF] Tyson | Palynofacies analysis[END_REF][START_REF] Zhang | Palynofacies and geochemical analysis of the Triassic Yanchang Formation, Ordos Basin: Implications for hydrocarbon generation potential and the paleoenvironment of continental source rocks[END_REF]. The different assemblages of refractory particulate organic matter permit to record environmental evolution and depositional characteristics. In particular, the different distributions can reflect the conditions of the oxygenation [START_REF] Tyson | Palynofacies analysis[END_REF][START_REF] Disnar | Soil organic matter (SOM) characterization by Rock-Eval pyrolysis : scope and limitations[END_REF], Di-Giovanni et al. 1999a). As mentioned in the geological setting, the Gault Clay was deposited in an open marine environment [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]. Indeed, the presence of Glauconie, Siderite and Pyrite are characteristic of an anoxic marine deposition at shallow depth. In our study, AUB230 (at 55-68 m) J o u r n a l P r e -p r o o f and the AUB240 samples present the well-preserved palynofacies assemblage. These samples show the presence of AOM with pyrite in inclusion (Fig. 7b,c). [START_REF] Tyson | Palynofacies analysis[END_REF], Boussafir et al 1995a, b) showed that the presence of gel-like AOM is generally associated with high preservation rates and low energy environments and result to anoxic deposits. This OM is similar to that observed in Kimmeridgian clays Formation (Boussafir et al, 1995, a, b, Boussafir et al. 1997) and has an ultrafine monoscopically amorphous structure derived from the preservation by natural sulfuration in an anoxic environment. The H2S produced during the sulphate-reduction process allows the formation of pyrite in association with the iron present in the sediments and preserve a part of the initially metabolizable OM and therefore becomes resistant to degradation and oxidation. This process is at the origin of the highly stabilized nature of the OM of these clays. Consequently, the OM of Tégulines Clay is insensitive to physicochemical conditions and would probably not have a direct action on the redox system of this clay formation.

Molecular investigation in Tégulines Clay OM

Total lipids extract

Tégulines Clay samples from the AUB230 borehole were selected for the molecular investigation of organic matter, based on S1 (> 0) and TOC values (~0.2) of the RE results.

The extract concentrations in Tégulines Clay are characterized by low content in labile compounds (0.3 to 1.0 mg.g -1 of dry sediment), and are consistent with the Rock-Eval quantitative (TOC) and qualitative (HI and OI) parameters and the palynofaciès composition (supplementary data 1), indicating the immaturity of OM (low free HC) and preserved insoluble kerogen. The extract concentrations in Tégulines Clay samples from the AUB240 and AUB1010 boreholes are very low and close to 0 mg/g (Rock-Eval ,S1, supplementary data 1), giving evidence of refractory and residual OM essentially.

Chromatograms patterns: n-alkanes

The molecular composition of the Tégulines Clay samples for the AUB230 borehole was investigated.

Three chromatograms patterns are presented in Figure 8 (sample at 6.10 m representing the oxidized area, sample at 25 m and, sample at 66 m representing preserved area). Very few compounds are present J o u r n a l P r e -p r o o f in the different samples. Phthalates compounds were found in the samples (55 -60 min retention time). the origin of these phthalates is unknown and could be the result of the extremely low concentration of natural organic compounds in the samples that could exacerbate the phthalates peaks and are not related to laboratory contamination. Several steroids were also encountered. In the biosphere, sterols detain essentially 27, 28 and 29 C atoms. C27-sterols produced by animals and C28-sterols produced by microalgae and fungi, C29-sterols are synthesized by land plants [START_REF] J O U R N A L P R E -P R O O F Huang | Sterols as ecological indicators[END_REF][START_REF] Volkman | A review of sterol markers for marine and terrigenous organic matter[END_REF]). The samples from the top and intermediate depths (6.10 m to 45 m) are composed of sitosterol, sitostanol, cholesterol, cholestanol coprostanol and epi-coprostanol. These sterols have a terrigenous origin. The end of the borehole is exempt from sterols.

This study mainly focuses on the alkanes composition in the different samples as they are more abundant and can lead to several calculations such as the Carbon Preference Index (CPI). The n-Alkanes are ubiquitous in the environment and are directly synthetized by living organisms or derived from straightchain biolipids [START_REF] Eglinton | Leaf epicuticular waxes[END_REF]. They can be used to discriminate the sources and the preservation of the sedimentary immature OM [START_REF] Brocks | Sedimentary hydrocarbons, biomarkers for early life[END_REF].

The total abundance of n-Alkanes varies between 0.29 and 9.14 µg/g sed, and increases from the bottom to the top of the clay formation (Table 4). In the AUB230 borehole, n-alkanes were dominated by n-C29 to n-C33 (Fig. 8) rather typical of terrestrial OM. The CPI defined by [START_REF] Bray | Distribution of n-paraffins as a clue to recognition of source beds[END_REF] was determined with the following equation: CPI = 2(odd n-C23 to n-C31) / (even n-C22 to n-C30 + even n-C24 to n-C32). The n-alkanes CPI index is generally interpreted in terms of the origin. A CPI ~ 1 indicates marine origin, whereas a CPI > 1 reflects more terrestrial contribution. Between 9.36 and 45 m, the CPI value is ~1.0 suggesting more marine contribution, however, this value could also reflect the oxidation of the OM. At the end of the borehole, the CPI is higher than 1, reflecting a mixture of marine and terrestrial organic compounds, more representative of the sedimentation conditions. CPI can also be used in order to characterize the degree of preservation of the n-alkanes in the sediments [START_REF] J O U R N A L P R E -P R O O F Xie | Molecular and isotopic stratigraphy in an ombrotrophic mire for paleoclimate reconstruction[END_REF][START_REF] Zheng | Lipid biomarkers in the Zoigê-Hongyuan peat deposit: indicators of Holocene climate changes in West China[END_REF][START_REF] Jansen | Methyl ketones in high altitude Ecuadorian Andosols confirm excellent conservation of plant-specific n-alkane patterns[END_REF][START_REF] Zhou | Postglacial climate-change record in biomarker lipid compositions of the Hani peat sequence, Northeastern China[END_REF][START_REF] Garel | Paleohydrological and paleoenvironmental changes recorded in terrestrial sediments of the Paleocene-Eocene boundary (Normandy, France)[END_REF]. CPI values between 3 and 10 refer to preserved OM. Values between 1 to 3 are the first signs of early degradation. Values close to 1 indicate more bacterial activity or recycled OM. At the start of the diagenesis, the molecular compounds are mainly composed of oxygen functional groups. During the diagenesis, the J o u r n a l P r e -p r o o f defunctionalization of the compounds leads at the end to the formation of hydrocarbons. The lipids that are stocked in the sediments lead to the loss of many compounds and short chains molecules are more degraded than the long chains ones.

The CPI values, calculated from the n-alkanes concentrations showed variations with depth. The CPI was high for the trench sample and decreased after to values around 1 (9.36 -21.30 meter deep). At the end of the borehole, the CPI values increased again. These features suggest more preserved OM at the top, in relation to the immature state of the OM, more degraded conditions between 9.36 and 21.30 m and again, more preserved conditions (or slightly degraded) at the end of the borehole. These results are in accordance with the RE and palynofacies results. The top of the AUB230 borehole is oxidized and after 21 m, more preserved OM is observed. However, the CPI ratio shows oxidized conditions until 21 m whereas the palynofacies and at a lesser extent, the RE data shows an oxidation profile until 10 m.

The CPI ratio is in accordance with the mineralogical data [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF] where the oxidation profile is observed until 21 m.

Comparison with other marine clay formations -Impact of the oxidation

From a general overview, the TOC values show that the Tégulines Clay are very poor in organic content. [START_REF] Guo | Mobility of organic compounds in a soft clay-rich rock (Tégulines clay, France)[END_REF] also studied the Tégulines clay in order to investigate the mobility of organic compounds in this formation. Despite a low TOC content (as observed in this study), they observed the retention of certain compounds such as lipophilic compounds. Other marine clay-rich formations that have experimented low temperature such as Tégulines Clay have been extensively investigated in the literature concerning their organic matter composition and variations. The Opalinus Clay from northern Switzerland did not display a higher temperature of burial than 85 °C [START_REF] J O U R N A L P R E -P R O O F Elie | Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland[END_REF]. They also display quite low C contents from 0.1 to 1 wt% (Todorof et al. 1993;[START_REF] Nagra | Project Opalinus Clay[END_REF]. Callovo-Oxfordian claystones is another formation, located in the Eastern part of the Paris basin, that experienced low temperature (50 °C) [START_REF] Landais | Utilisation de la géochimie organique pour la détermination du paléoenvironnement et de la paléothermicité dans le Callovo-Oxfordien du site de l'Est de la France[END_REF]. Their total organic C content is also generally low (<1 wt.% of the bulk rock). The Tmax recorded for the Tégulines Clays is essentially < 430 °C. This temperature is revealing immature OM. The RE Tmax of the Opalinus Clay also displays temperatures J o u r n a l P r e -p r o o f ≤435 °C in accordance with low thermal maturity. The thermal immaturity of the Callovo-Oxfordian formations was demonstrated by the predominance of odd/even long-chain n-alkanes with CPI higher than 2 [START_REF] Hautevelle | Tracing of variabilities within a geological barrier by molecular organic geochemistry. Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)[END_REF]). In the case of the Tégulines Clay, the CPI cannot estimate the immaturity as most of the formation is under oxidation. However, CPI can be used for the estimation of the preservation. Our study emphases that the RE technique is suited to be used for oxidized formations.

The HI versus OI plot (pseudo Van Krevelen plot, Fig. 4) is usually employed to separate the marine and terrestrial contributions in preserved conditions. In [START_REF] J O U R N A L P R E -P R O O F Elie | Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland[END_REF], the Opalinus Clay falls into the Type III kerogen area, revealing more terrestrial contribution. The Callovo-Oxfordian formations van Krevelen diagram indicate type II and III OM mixture, showing a marine origin, with a contribution of terrestrial-derived materials [START_REF] Disnar | Sédimentation de la matière organique dans le nord-est du Bassin de Paris: conséquences sur le dépôt des argilites carbonées du Toarcien inférieur (Organic matter sedimentation in the northeast of the Paris Basin: consequences on the deposition of the lower toarcian black shales)[END_REF][START_REF] Hautevelle | Vascular plant biomarkers as proxies for palaeoflora and palaeoclimatic changes at the Dogger/Malm transition of the Paris Basin (France)[END_REF]. For the Tégulines Clay, no conclusion permits to settle between marine or terrestrial contribution because the HI and OI values can also suggest the presence of oxidized marine contribution, leading to the transfer to the type III kerogen area.

The molecular investigation of the Tégulines Clay seems also to be perturbed by the oxidation profile.

The yields of OM extract in Tégulines Clay are low 0.3 to 1.0 mg. g -1 of dry sediment. By comparison, the extract yield for Opalinus Clay is comprised of 0.9 and 48 mg. g -1 [START_REF] J O U R N A L P R E -P R O O F Elie | Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland[END_REF]. The yield fractions of soluble OM ranges between 0.01 and 0.65 mg of organic extract/g of rock for the Callovo-Oxfordian formations [START_REF] Hautevelle | Tracing of variabilities within a geological barrier by molecular organic geochemistry. Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)[END_REF]). Despite the low yield of soluble OM, Callovo-Oxfordian formations displayed a large variety of compounds deciphered by GCMS (n-alkanes, steroids, hopanoids among others), permitting to get information on the OM maturity and origin. In contrast, the chromatograms patterns of the different samples from the AUB230 borehole show the presence of a low number of peaks, revealing a low number of molecular compounds (Fig. 8). Only n-alkanes could be easily deciphered. However, the results concerning the n-alkanes distribution and the CPI are questionable. Indeed, the predominant n-alkanes are ranging between C29 and C33, revealing terrestrial origin such as for the Opalinus Clay (Odd/Even predominance of C25-C35 range [START_REF] J O U R N A L P R E -P R O O F Elie | Biomarker transformations as constraints for the depositional environment and for maximum temperatures during burial of Opalinus Clay and Posidonia Shale in northern Switzerland[END_REF]). By contrast, the Tegulines CPI is ~ 1 revealing marine origin. These opposite results could stem from an artifact caused by the oxidation of the OM, shifting the short-chain of n-alkanes. These results can question the use of certain techniques when dealing with oxidized OM.

J o u r n a l P r e -p r o o f

Comparison of the TCF OM with mineralogical and dissolved inorganic carbon (DIC) changes through the TCF weathering profile

In this study, the AUB230 borehole enabled to evidence the three main facies (from the bottom to the top: UAQ, UA, and UAC units, see §2.1.) that can be encountered in the TCF, whereas the AUB1010 borehole only crosscut the UAQ and UA units [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]. In the both boreholes, the oxidation profile was observed between the sub-surface and ~21 m depth [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF][START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]) (Fig. 9).

The brown and granulous textures, the bulk and molecular characteristics of the OM at the surface (0-30 cm borehole AUB230) revealed high amounts of organic matter showing typical oxidative degradation in soil, according to the following reaction: CH2O + O2 = H2O + CO2. These observations are in good agreement with the DIC of 1.4 mEq/L measured in soil pore waters, the high CO2 soil degassing and the low δ 13 C value of degassed CO2 (-25.5 ‰ PDB) [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF].

Between 30 cm and 5 m deep in the AUB230 borehole, in ocher carbonate-free sandy clay loams overlying TCF, the bulk and OI index of the OM gave evidence of extremely low TOC contents and high oxidative conditions consistent with the altered pedogenetic OM surficial bring (Fig. 4). These observations are in good agreement with the low DIC (<0.9 mEq/L) measured in pore waters and the low δ 13 C values of DIC (~ -21 ‰ PDB) [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF].

Below ~5 m in the AUB 230 borehole and ~2-3 m in AUB1010 borehole, the top of TCF is ocher, plastic and marked by an intense and visible oxidation of pyrite and other iron-bearing minerals (iron-rich clays, ankerite) that decreases down to 11 m depth. Pyrite oxidation leads to iron oxyhydroxide and gypsum precipitation, but also to a small calcite dissolution due to slight acid pH. Ankerite oxidation leads to iron oxyhydroxide precipitation. The clay fraction in TCF is quite homogeneous and composed by ~16±5 % of detrital kaolinite, ~16±4 % of illite-smectite, ~12±5 % of illite-mica, and minor chlorite (<2 %), and ~8±6 % of diagenetic glauconite. The study of clay minerals in the 5-10 m zone, based on microscopic observations, XRD and electron microprobe gave evidence of a change of color from greenish to ocher due to oxidation of iron, a loss of iron to form iron oxides and an increase of the smectite component, in particular concerning chlorite and glauconite [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF][START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]. In the same way, the OI of the OM is high and confirms oxidative conditions. Combined mineralogical and OM data are consistent with the high DIC values (up to 8.5-8.6 mEq/L) measured in Tegulines Clay J o u r n a l P r e -p r o o f pore waters in the 5-10 m zone of the both AUB230 and AUB1010 borehole. The δ 13 C values of degassed CO2 (-19.5 to -12.9 ‰ PDB) corresponds to a mixing between OM matter degradation and CO2 due to calcite dissolution [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]. The OM study gave a supplementary information with the OI index, which is consistent with a mixing of the altered pedogenetic OM surficial supply and the oxidation of original organo-clays fraction of the initial marine sediments (Fig. 4). The identification of OM surficial supply down to ~9-10 m is in good agreement with the rare presence of small roots down to 10-12 m in boreholes [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF]. The oxidation of pristine marine OM down to ~9-10 m in the weathering profile is also an important point, which is a subject of debate for chemical modelling of weathering profile in marine clay formations [START_REF] Bao | Modeling controls on the chemical weathering of marine mudrocks from the Middle Jurassic in Southern Germany[END_REF].

Between 9-10 m and 55 m, the OM oxidation state was homogenous and low, whereas changes of consistency from plastic to hard and of mineralogy (slight oxidation of glauconite marked by yellowish color) were still observed at ~ 20-25 m [START_REF] Debure | Retention of arsenic, chromium and boron on an outcropping clay-rich rock formation (the Tégulines Clay, eastern France)[END_REF][START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]. The variation between plastic/non plastic behavior of the TCF seems to not play a role for OM preservation.

The bottom of the TCF evolved under reducing conditions, and are characterized by an enrichment in clay minerals, including glauconite and smectite [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF]. The OM data also showed more preserved OM with higher HI, the microscopic data also show more preserved conditions with higher grAOM and OgAOM contents with the inclusion of pyrite suggesting the role of bacterial sulphate reduction in an anoxic sedimentary environment. Indeed, the association of pyrite with the amorphous orange gel-like organic matter is interpreted as a non-biodegradable and stable organic matter preserved by incorporation of sulfur by natural sulfurization [START_REF] Boussafir | Structure ultrafine de la matière organique des roches mères du Kimméridgien du Yorkshire[END_REF](Boussafir et al. , 1995[START_REF] Boussafir | Accumulation of Organic Matter in the Kimmeridge Clay Formation (KCF): An Update Fossilisation Model for Marine Petroleum Source-Rocks[END_REF].

At interface with the Greensand, TCF shows a drop of the TOC, S1, S2 and an increase of OI (Supplementary data 1). The green sand detains coarser particles than the Tégulines Clay and could store and/or preserve less OM.

Overall, the OM characterization (RE, palynofacies) of TCF in the different boreholes supports a welldeveloped oxidation profile in the ~ 0-10 m and preservation of reduced conditions in the deeper parts, in agreement with the previous mineralogical and geochemical studies. As for sulfur and iron oxidation states, the oxidized or preserved state of the OM will finally help to redox regulation with depth in the Tégulines Clay. Indeed, despite a similar TOC content all along the investigated boreholes, the J o u r n a l P r e -p r o o f preservation of the organic matter and especially its reducing capacity will be one of the parameters that might influence the mobility of sensitive-redox chemical elements [START_REF] Debure | Retention of arsenic, chromium and boron on an outcropping clay-rich rock formation (the Tégulines Clay, eastern France)[END_REF][START_REF] Debure | Influence of soil redox state on mercury sorption and reduction capacity[END_REF]. The small amount of preserved, very little functionalized and unreactive OM and the refractoriness and stability of OM of almost all the borehole samples studied plead for a slight influence of OM in the Tégulines in a redox system.

Clay minerals, and particularly smectite, can physically protect the OM in these sediments [START_REF] Hedges | Comparative organic geochemistries of soils and marine sediments[END_REF][START_REF] Nelson | Dispersed clay and organic matter in soil: their nature and associations[END_REF][START_REF] Drouin | Carboxylic acid sorption on synthetic clays in sea water: In vitro experiments and implications for organo-clay behaviour under marine conditions[END_REF][START_REF] Mahamat | Organic matter-clay interaction along a seawater column of the Eastern Pacific upwelling system (Antofagasta bay, Chile): Implications for source rock organic matter preservation[END_REF]). The comparison with the organic data (TOC, HI, OI) shows that we have, at the bottom of the borehole an increase of clay minerals, including smectite / smectite-illite and glauconite, and an IH increase. [START_REF] Bruun | Lability of soil organic carbon in tropical soils with different clay minerals[END_REF] stated that smectite have higher capacity to stabilize organic matter than illite due to higher specific surface area and cation exchange capacity. All these information permits to state that the protection of the organic matter at the bottom of the AUB230 borehole (66 -68 m) can be the presence of smectite in higher proportion.

The OM is preserved in the AUB240 borehole while it was more oxidized in the AUB1010 at least between 3 and 16 m and also observed from mineral characterizations. The OM preservation is higher in the AUB240 borehole, as a 12 m layer of Brienne Marls overlies it themselves covered by 8 m of surficial layers (loess, clay sediments and carbonated alluvium). By contrast, the surficial layer in the AUB230 borehole represents only 5 m and even less (3 m) in the AUB1010 borehole. Therefore, meteoric water reaches faster the Tégulines in the AUB1010 and AUB230 boreholes. Finally, the difference between the AUB230 and the AUB1010 borehole relies on their position in the valley. The AUB230 borehole is located at the hilltop while the AUB1010 is located at the bottom where the water can stream from the hills. The position of the AUB1010 borehole is therefore favorable to a higher alteration compared to the other boreholes and all these characteristics explain the higher oxidation depth observed for organic matter in that borehole.

J o u r n a l P r e -p r o o f Conclusion

This study investigated the OM composition of the Tégulines Clay formation using bulk, microscopic and molecular techniques. All the profiles studied show that Tégulines Clay are poor in organic content in general. The bulk results using RE analyses revealed that the OM of all clays studied samples was immature. The RE parameters, deconvolution of S2 peak, R400, palynofacies and molecular investigations were all positively correlated. Indeed, at the surface (TPH1-1 0-30), the OM showed relatively high HI and TOC with a large amount of preserved particles revealing typical soil litter OM.

The deconvolution of the S2 peak curve showed a dominant contribution of the C3 cluster that is typical of the breakdown of polysaccharides and lignin in the surface part of the studied profile. The other trench samples collected below 30 cm showed very oxidized conditions (low TOC and high OI). The AUB240 borehole, from the bulk and microscopic investigation, revealed more preserved conditions, mainly due to the overlaying of the Brienne marls and is presented as a reference borehole in term of OM preservation. The investigation of the AUB230 borehole clearly showed an oxidation profile at the top and more pristine, preserved and reductive conditions deeper. The AUB1010 borehole showed similar conditions to the AUB230 borehole but a higher oxidation depth. These different oxidation depths could be explained by the different spatial topological location of the boreholes. This study showed that the Tégulines Clay OM is: very low in amount, stable in its preserved section, essentially residual and littlesensitive to the biotic and abiotic degradation and thus would be very weakly reactive. The OM influence would also be limited in a redox system supporting previous results obtained on the behavior of sensitive-redox chemical elements. Finally, this is supported on the one hand by the small amount of preserved, very little functionalized and unreactive OM and on the other hand, by the refractoriness and stability of OM of almost all the borehole samples studied. This study also shows that a good set of techniques permit to deal with the complex atmosphere / Geological formations interactions in the critical zone. (6.10, 18.22, 25.32, 45.84, 67.45 m and comparison with the TPH1-1 0-30)

J o u r n a l P r e -p r o o f compared with mineral changes [START_REF] Lerouge | A deep alteration and oxidation profile in a shallow clay aquitard : example of the Tégulines Clay[END_REF], dissolved inorganic carbon concentration (DIC) in pore waters (PW) and contribution of degradation of organic matter (OM) to the DIC [START_REF] Lerouge | Origin of dissolved gas (CO2, O2, N2, alkanes) in pore waters of a clay formation in the critical zone (Tégulines Clay, France)[END_REF].

J o u r n a l P r e -p r o o f

  Amorphous Organic Matter Diffuse limits, grey to yellow in transmitted light, opaque or slight orange in reflected light, size: 10-100 µm gAOM: Gelified Amorphous Organic Matter Particle entirely gelified, no internal structure, orange to red in transmitted light, dark orange in reflected light, size: can reach very large size over 100 µm Gd: Gelified debris Sharp contours, high reflectance, size: 10 µm Od: Opaque debris Sharp contours, high reflectance, dark in transmitted light, size: 10 µm Plc: Preserved lignocellulosic Elongated particles with visible internal structures, yellow in transmitted light (10-100 µm) Salc: Slightly amorphised lignocellulosic Elongated particles with visible internal structures, yellow to orange in transmitted light (10-100 µm), trace of gelification Glc: Gelified lignocellulosic Elongated particles with visible internal structures, yellow to orange in transmitted light (10-100 µm), higher state of gelification Olc: Opaque lignocellulosic No internal structure visible, elongated, show high reflectance (10-100 µm) Div: divers Mycelium fragments: elongated particles, brown color; Cuticular fragments: particles with homogeneous limits, brown, with typical botanic structures, size variable and can exceed several hundred µm; Spores and pollens: particles from the terrestrial and aquatic flora, translucent or yellow for fresh particles and brown-orange for preserved particles; acritarchs, foraminifera pyrite framboidal, opaque, with geometrical forms under transmitted light Amorphous particles Ligno cellulosic debris Other organic particles J o u r n a l P r e -p r o o f

Fig. 1

 1 Fig. 1 (a) Geological map of the east part of the Paris Basin showing the studied area; (b) Geological map of the studied area showing the location of the AUB240, AUB230 and AUB1010 boreholes selected for the organic matter study; (c) Major mineralogy of the Tégulines clay from the AUB230 and AUB1010 boreholes deduced from XRD data treatment, compared with previous data of AUB111 and AUB121 boreholes (Lerouge et al., 2018); UA: clay rich unit; UAC: carbonate-clay rick unit; UAQ: clay-quartz rich unit

Fig. 2

 2 Fig.2The different categories of particulate organic matter distinguished from their morphology, the scale of the white bars corresponds to 100 µm; Ligno-cellulosic fragments: -preserved ligno-cellulosic fragments (plc),-slightly degraded lignocellulosic fragments (slc), -gelified ligno-cellulosic fragments (glc),-opaque ligno-cellulosic fragments (olc); amorphous particles: -granular amorphous organic matter (grAOM),-gelified amorphous organic matter (gAOM),-gelified debris (gd),-opaque debris (od); Others organic particles: -mycelium fragments (Myc); -foraminifera, -cuticular fragments (Cut), -Spores and pollens (sp), -(c) Pyrite.

Fig. 3

 3 Fig.3Total Organic Carbon (TOC, %), Hydrogen Index (HI, mg HC.g -1 TOC), and Oxygen Index (OI, mg CO2.g -1 TOC) in relation with depth for the AUB240, AUB230 and AUB1010 boreholes.

Fig. 5 Fig. 6

 56 Fig. 5 Deconvolution of multilobed S2 signals from RE pyrolysis for a TPH1-1 030 (r 2 = 0.996), b AUB240 39 (r 2 = 0.999), c AUB230 6.10 (r 2 = 0.994), d AUB230 25.32 (r 2 = 0.997), e AUB230 67.45 (r2 = 0.998), f AUB1010 1.88 (r 2 = 0.974), g AUB1010 3.31 (r 2 = 0.996), h AUB1010 14.47 (r 2 = 0.998), i AUB1010 20.95 (r 2 = 0.995). Black-grey curves are the rebuilt S2 signal from deconvolution.

Fig. 7

 7 Fig. 7 Distribution of the different particles in: (a) TPH1-1 0-30 sample; (b) AUB240 borehole (29,39,70 and 80 m deep); (c) AUB230 borehole(6.10, 18.22, 25.32, 45.84,

Fig. 8

 8 Fig. 8 Chromatograms of the Tégulines Clay formation at 67 m; 25 m and 6.10 m

Fig. 9

 9 Fig. 9 Main characteristics of the organic matter through the weathering profile developed in Tégulines clay,

Table 2

 2 Distributions, abundances and ratios of n-alkanes in the Trench TPH1-1 (0 -30 cm sample) and AUB230 borehole. Majors n-alkanes in core samples, b Total = total abundance of n-alkanes (µg/g sediment), c odd/even ratio (odd/even = ∑conc. odd alkanes /∑conc. even n-alkanes) d n-alkanes carbon preference index CPI = 2(odd n-C23 to n-C31)/(even n-C22 to n-C30+ even n-C24 to n-C32).

			Total of alkanes
		Major alkanes a	(µg/g sed) b	odd/even c	CPI d
	TPH1-1 0-
	30cm	n-C29, n-C31, n-C33	5.08	2.97	4.95
	AUB230
	9.36m	n-C29, n-C31, n-C33	9.14	1.26	1.08
	AUB230
	21.30m	n-C29, n-C31, n-C33	0.95	1.06	0.97
	AUb230
	25.32m AUB230 45.84m AUB230 66.35m AUB230 67.45m J o u r n a l P r e -p r o o f n-C29, n-C29, n-C31 0.61 1.37 n-C29, n-C31, n-C33 0.56 1.34 n-C29, n-C31, n-C33 0.47 0.97 n-C25, n-C31, n-C31 0.29 1.27	1.19 1.15 1.57 1.74

a

Acknowledgements

J o u r n a l P r e -p r o o f

This study was supported financially by the French National Agency for Radioactive Waste Management (Andra) and the French Geological Survey (BRGM). The authors want to acknowledge Rachel Boscardin and Marielle Hatton for their technical support as well as the associate editor and the two anonymous reviewers J o u r n a l P r e -p r o o f -OM characterization of the Tégulines Clay formation using bulk and molecular data -Vertical variation of the oxidation profile as a result to the vicinity to the surface -First upper 10 m of the clays subjected to oxidative events, below 10 m OM preserved -Spatial variations of the oxidation state due to different topography of the boreholes -OM bulk and molecular techniques are a good association for critical zone studies J o u r n a l P r e -p r o o f

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.