# Tracing the sedimentary provenance of the Mesoproterozoic rocks from Taoudeni Basin (~1.1 Ga) Mauritania: Evidence from Sm/Nd and elemental geochemistry

Mohamed Ghnahalla, Olabode Bankole, Ahmed Abd Elmola, Marc Poujol, Claude Fontaine, Mohamed Salem Sabar, Alain Trentesaux, Chenyi Tu, Timothy Lyons, Abderrazak El Albani

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Mohamed Ghnahalla, Olabode Bankole, Ahmed Abd Elmola, Marc Poujol, Claude Fontaine, et al. Tracing the sedimentary provenance of the Mesoproterozoic rocks from Taoudeni Basin (~1.1 Ga) Mauritania: Evidence from Sm/Nd and elemental geochemistry. Precambrian Research, 2023, 388, pp.107003. 10.1016/j.precamres.2023.107003. insu-04017215

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1 Tracing the sedimentary provenance of the Mesoproterozoic rocks from Taoudeni Basin

2 (~1.1 Ga) Mauritania: Evidence from Sm/Nd and elemental geochemistry.

3 Mohamed Ghnahalla<sup>a,c</sup>, Olabode M. Bankole<sup>a</sup>, Ahmed Abd Elmola<sup>a</sup>, Marc Poujol<sup>b</sup>, Claude

4 Fontaine<sup>a</sup>, Mohamed Salem Sabar<sup>c</sup>, Alain Trentesaux<sup>d</sup>, Chenyi Tu<sup>e</sup>, Timothy W. Lyons<sup>e</sup> and

5 Abderrazak El Albani<sup>a,*</sup>

6

7 <sup>a</sup>University of Poitiers, UMR 7285 CNRS, IC2MP, 5, Rue Albert Turpin, F-86073, Poitiers

8 Cedex 9, France

9 <sup>c</sup>University of Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France

10 <sup>b</sup>Department of Geology, FST, University of Nouakchott Al-Aasriya, BP 5026, Nouakchott,

11 Mauritania

12 <sup>d</sup>UMR 8187 LOG CNRS, University of Lille, ULCO, 59655 Villeneuve d'Ascq, France

13 <sup>e</sup>Department of Earth and Planetary Sciences, University of California, Riverside, Riverside,

14 CA, United States

15 *Corresponding author.

16 E-mail address: abder.albani@univ-poitiers.fr (A. El Albani)

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23 Abstract

The Mesoproterozoic era is a crucial period in Earth history characterized by muted oxygen levels in the atmosphere-ocean system. This period is well represented in the non-metamorphosed sedimentary rocks from the Taoudeni Basin, Mauritania. Few studies have been carried out to trace the sources of these sedimentary archives. Here, we examined the sedimentary rocks from the Atar (S4 drill core) and El Mreiti groups (S2 and S3 drill cores).

This study focuses on whole-rock elemental geochemistry and Sm/Nd isotope compositions to provide insights into the provenance of the fine-grained siliciclastic sediments from the basal part of the Mesoproterozoic Atar and El Mreiti groups. Paleoweathering indices reveal a moderate degree of chemical weathering in the source areas, consistent with the low compositional maturity of the studied samples. The concentrations of the relatively immobile trace elements suggest mixing sources of sediment provenance, which is dominated by felsic source rocks for the Atar sediments. However, distinctively positive ε$_{Nd(t)}$ values coupled with high ¹⁴³Nd/¹⁴⁴Nd and Sm/Nd ratios and high fSm/Nd values of the sediments from the El Mreiti Group indicate derivation from juvenile and less evolved source rocks. Further, the depleted mantle model ages (T$_{DM}$) of the provenance protolith (1.95-2.31 Ga) support the argument that the El Mreiti sediments are dominantly sourced from the Paleoproterozoic terrane exposed in the eastern Reguibat Shield while the Atar Group were predominantly from the Archean basement rocks in the western Reguibat Shield. Moreover, Sm/Nd isotope and mixing model results support the major contributions of the felsic Archean rocks of the Reguibat shield for the Atar Group samples. Although these strata, separated by ~1000 km, have been described as stratigraphic equivalent, our study demonstrates distinct sediment sources between the Atar Group strata and those of El Mreiti, therefore, reinforcing the importance of sediment provenance in understanding the evolution and reconstruction of modern and ancient sedimentary systems.
Keywords: Elemental geochemistry, Nd isotope, Provenance, Mesoproterozoic, Taoudeni Basin, Mauritania.

# 1. Introduction

The provenance of sediment, tectonic setting, timing of sedimentation, and post-depositional history play a crucial role in revealing the geological histories of ancient sedimentary basins (Bhatia and Crook, 1986; McLennan and Hemming, 1992). The mineral, elemental, isotopic, and geochemical compositions of fine-grained sediments have been widely used to shed light on the hydraulic sorting, paleoweathering conditions, potential source rocks, and the tectonic evolution of sedimentary basins (Bhatia and Crook, 1986; Cullers, 1994; DePaolo et al., 1991; McLennan et al., 1993; Nagarajan et al., 2017; Nesbitt and Young, 1982). In particular, the relatively immobile trace elements and Sm-Nd isotopic compositions are useful to track crustal evolution, provenance, tectonic regimes, and age of mantle derivation of the source rocks in sedimentary basins (McLennan et al., 1993). Understandably, the chemical and mineralogical compositions of sedimentary rocks along the way from source to sink are controlled by their provenance, tectonic settings, climate, biological processes, depositional sedimentary (e.g., weathering, transport, and erosion), and post-depositional (diagenesis/lithification, metamorphism, and hydrothermal) processes (Bhatia and Crook, 1986; Fedo et al., 1995; McLennan et al., 1993; Nesbitt and Young, 1982). Most major elements such as Ca, Fe, Mg, Na, and K are mobile during sedimentary processes, thus are not reliable for provenance analyses of these sedimentary rocks (McLennan et al., 1993). However, some trace elements such as Th, Sc, Zr, and REEs have been widely applied to provenance reconstructions because of their relative immobility, short residence times in seawater, and resistance to fractionation during sedimentary processes and are therefore believed to be quantitatively transported into sedimentary basins (Cullers, 1994; McLennan et al., 1993).
The Taoudeni Basin, the focus of this study, is located in North Africa (Fig. 1), extending across large parts of Mauritania and Mali and portions of Algeria, Guinea, Senegal, and Sierra Leone (O'Connor et al., 2004). The basin is known as one of the largest Mesoproterozoic and Paleozoic sedimentary basins in North Africa (Lahondère et al., 2003). In Mauritania, the basal parts of the Mesoproterozoic strata of the Atar and El Mreiti groups are exceptionally preserved and crop out along the northern edge of the Taoudeni Basin (Kah et al., 2012; Ghnahalla et al., 2022a; Tu et al., 2022; Ghnahalla et al., 2022b). Although several studies relevant to paleoenvironmental reconstructions have been carried out on the sediments (Gilleaudeau and Kah, 2015, 2013; Kah et al., 2012), less attention was paid to the origin of the sediments from the Atar and El Mreiti groups. Here, we present a detailed study involving new whole-rock elemental and Sm/Nd isotope composition for the basal sedimentary units of the Atar and El Mreiti groups from the Taoudeni Basin in Mauritania. The main objective is to investigate the paleoweathering, potential provenance, and tectonic setting of fine-grained siliciclastic rocks. First, we evaluated the influence of sedimentary processes on the elemental compositions before using them to track sediment provenance. Therefore, an integrated approach using the least-mobile trace element and Nd isotope model ages can potentially illuminate the time-varying changes of the sedimentary source and the related tectonic settings.

## 2. Geological background

The Archean - Paleoproterozoic West African Craton (WAC; Fig. 1) represents a large area that extends across northwestern Africa (Potrel et al., 1996). The WAC rocks mainly outcrop as Reguibat and Man-Léo shields in the north and south, respectively, which are the main sources of the sedimentary rocks of the Taoudeni Basin (Bertrand-Sarfati et al., 1991). The Reguibat Shield separates the Taoudeni and Tindouf sedimentary basins, covering much of southwest to northeast Mauritania (Bertrand-Sarfati et al., 1991; O'Connor et al., 2004).
Studies on the Reguibat Shield have recognized two sectors, a western Archean terrane dominated by gneisses and granitic rocks and an eastern part largely composed of granitic, basaltic, and metasedimentary rocks of Paleoproterozoic (Birimian) terrane (Pitfield et al., 2004; Schofield et al., 2006). These compartments of juvenile Paleoproterozoic supracrustal rocks were juxtaposed against the Archean crystalline basement during the Eburnean Orogeny (Schofield et al., 2006). The Birimian in the WAC generally refers to rocks of the early Paleoproterozoic age (2.5 - 2.0 Ga), which were affected by the tectonic-metamorphic activity (2.1–2.0 Ga) of the Eburnean orogeny (Abouchami et al., 1990; Schofield et al., 2006).

The Archean domain of the Reguibat Shield experienced a complex history of magmatism and polyphase orogeneses, such as the marked collision at 2.95 Ga between the Choum-Rag el Abiod and Tasiast-Tijirit terranes. The Choum-Rag el Abiod Terrane corresponds to the remnant of a deeply eroded Archean crust dominated by greenstone remnants in migmatitic gneisses and metamorphic rocks of the Mesoarchean Amsaga complex and intruded granitic and less commonly metabasic bodies (Pitfield et al., 2004). The Amsaga complex (TDM age = 3.6-2.9 Ga), is dominated by granulite-facies, migmatitic, and metamorphic rocks, as well as intruded granitic and metabasic bodies (Potrel et al., 1998; Key et al., 2008; Montero et al., 2016; O'Connor et al., 2004). The Tasiast-Tijirit terrane (TDM age = 3.6-3.1 Ga) occupies the western part of the Archean terrane and is composed mainly of greenstone belts, granites, and gneiss assemblages (Key et al., 2008; Pitfield et al., 2004). The Paleoproterozoic (Birimian) terrane is preserved in the eastern Reguibat Shield in Mauritania and is mainly composed of granitoids, metamorphosed tholeiitic basalt, sedimentary and low-grade metavolcanic lithologies, and metasediments within the remnants of the Archean basement rocks (Abouchami et al., 1990; Boher et al., 1992). Geochronological data from the granites and Tsalabya tholeiitic lavas of the Birimian terrane of the Reguibat Shield recorded
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TDM ages of 2.19-1.83 Ga and Sm-Nd isochrons at 2.22 Ga (Abouchami et al., 1990; Boher et al., 1992).

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The Taoudeni Basin is one of the largest Mesoproterozoic to Cretaceous intracratonic basins covering much of the WAC (Lahondère et al., 2003). It rests, with a major unconformity, on the metamorphic and granitic basement rocks of the Reguibat Shield (Bertrand-Sarfati et al., 1991; Lahondère et al., 2003; O'Connor et al., 2004). The cratonic sedimentary cover of the Taoudeni Basin records a discontinuous history of sedimentation dominated by shallow marine and/or continental siliciclastic deposits and subordinate shallow marine carbonates (Bertrand-Sarfati et al., 1991). The sedimentary strata of the Taoudeni Basin have been subdivided into three major supergroups bounded by craton-scale unconformities – the Hodh Supergroup (Meso- to Neoproterozoic), Adrar Supergroup (Neoproterozoic/Cambrian), and Dahr Supergroup (upper Ordovician to Carboniferous) (Lahondère et al., 2003; Pitfield et al., 2004).

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The sedimentary deposits of the Taoudeni Basin begin with the oldest stratigraphic unit of the Char Group that directly overlies the Amsaga complex rocks. The Char Group consists of coarse- to fine-grained siliciclastic sediments and subordinate carbonates interpreted as fluvial, coastal aeolian, and shallow marine deposits (Benan, 1998). The overlying Atar, El Mreiti, and Assabet el Hassiane groups constitute the unconformity-bounded units of the thick succession of gently dipping Proterozoic strata (Lahondère et al., 2003; Pitfield et al., 2004). The late Mesoproterozoic (~1.1 Ga) sedimentary deposits of the Atar and El Mreiti groups rest unconformably on the Char Group strata and the basement rocks. The Atar and El Mreiti groups are composed of stromatolite-bearing carbonate and interbedded fine-grained siliciclastic deposits representing craton-wide flooding and deposition in shallow marine settings (Bertrand-Sarfati and Moussine-Pouchkine, 1988; Kah et al., 2012). The Atar and El Mreiti sediments were deposited in a shallow-water pericratonic

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environment and an epicratonic platform, respectively, thus providing a transect across
changing water depth (Kah et al., 2012). They are overlain by an erosional disconformity,
which is followed by marine fine-grained siliciclastic deposits of the Assabet el Hassiane
Group (Lahondère et al., 2003).

## 2.1. Stratigraphy and facies of the Atar Group

The Atar Group is a late Mesoproterozoic deposit of the Taoudeni Basin (Kah et al., 2012; Rooney et al., 2010). This Group is well-defined in the Adrar region. It is comprised of a ~750m-thick succession of alternating siliciclastics and carbonates, with variable contents of sandstone, siltstone, mudstone, and dolostone (O'Connor et al., 2004). The Atar Group is comprised of ten formations (Lahondère et al., 2003; O'Connor et al., 2004). The basal Foum Chor Formation lies on a sharp erosional base with conglomeratic sandstone (O'Connor et al., 2004). The lower part of the formation comprises a thick bed of coarse-grained sandstones, commonly with sharp erosional bases (Benan, 1998). The middle and uppermost part of the Foum Chor Formation is typically comprised of fine- to medium-grained and coarse-grained sandstones, respectively (Benan, 1998). The Ksar Torchane Formation comprises predominantly interbedded micaceous shale, siltstone, and occasional fine-grained sandstone. The formation marks declining siliciclastic influx into the shallow marine environment and the onset of microbial carbonate deposition within the middle and uppermost formation (Kah et al., 2012).

The overlying Tod Formation is comprised predominantly of pyritic shales, muddy siltstones, and interbedded carbonates. Three distinct stromatolitic reefs of herringbone-bearing carbonate, columnar stromatolitic growths, and stromatolitic bioerms characterize the formation (Kah et al., 2009). Dark to blue-grey shale, siltstone, sandstone, and subordinate carbonates of the Tarioufet Formation mark the expansion of siliciclastic materials into shallow marine settings. The mid-Oued Tarioufet Formation is characterized by regional
172 evaporite deposition, whereas the uppermost formation records a return to carbonate
173 deposition (Kah et al., 2012; O'Connor et al., 2004). The overlying Tawaz Formation
174 comprises mainly stromatolitic limestone and dolostone and subordinate shale. The formation
175 records widespread expansion of columnar to branching stromatolites and contains a
176 distinctively developed brecciated horizon (Bertrand-Sarfati and Moussine-Pouchkine, 1988;
177 Kah et al., 2012). The Terrarit Formation comprises predominantly shale, siltstone, sandstone,
178 and subordinate carbonates (O'Connor et al., 2004). The overlying Aouïnet Ould Bou
179 Derballa Formation displays a large-scale reef of domal and columnar stromatolitic limestone
180 and dolomitic limestone with subordinate shale. The d'Aouleïgate Formation comprises
181 glauconitic siltstone, micaceous sandstone, thinly interbedded mudstone, and subordinate
182 limestone. The topmost Touiderguilt and Tifounke formations are dominated by stromatolitic
183 carbonate with subordinate sandstones, siltstones, and shales (O'Connor et al., 2004).

184 2.2. Stratigraphy and facies of the El Mreiti Group

185 The El Mreiti Group, which represents the stratigraphic equivalent of the eastern Atar
186 Group, has been subdivided into eight formations representing various sedimentary
187 environments. The El Mreiti Group consists of siliciclastic and stromatolite-bearing
188 carbonates and reflects deposition beneath shallow waters over a stable craton during a global
189 sea-level highstand (Kah et al., 2012). The basal Khatt Formation is dominated by medium- to
190 coarse-grained sandstone and clayey siltstone of fluvial-deltaic, marine tidal-flat, and shallow
191 marine environments (Kah et al., 2012; Lahondère et al., 2003). The En Nesoar Formation is
192 characterized by interbedded shale, clay-rich siltstone, and clayey to stromatolitic limestone,
193 which were likely deposited in low-energy environments (Kah et al., 2012; Lahondère et al.,
194 2003).

195 The overlying Touirist Formation is characterized by a basal stromatolitic bioherm;
196 interbedded thin-bedded, clayey limestone; and organic-rich black shale deposited in a
predominantly shallow-marine environment (Kah et al., 2012; Lahondère et al., 2003). The overlying thick succession of the Aguelt el Mabha Formation consists of mudstone, shale, and clayey siltstone with varying carbonate contents. The Gouamir Formation marks the return to carbonate deposition, with numerous storm breccias and stromatolitic carbonates (Kah et al., 2012). The basal unit is characterized by massive and laminated dolomite and intercalated brecciated beds, whereas the upper unit displays more stromatolitic biostromes and relatively rare brecciated beds (Lahondère et al., 2003). The overlying Tenoumer Formation is comprised of dolostone, stromatolite bioherms, and minor glauconite sandstone. It is also characterized by storm deposits of thin carbonate breccia, flat pebbles, and conglomerates, (Lahondère et al., 2003). The Ligdam Formation consists of glauconitic sandstone with storm breccias and numerous stromatolites, whereas the overlying Elb Nous Formation consists mainly of sandstone and carbonate breccias with rare stromatolites (Lahondère et al., 2003).

## 3. Materials and methods

Seventy-eight representative samples have been analyzed. Most of them are black shales and siltstones of the lower Atar and El Mreiti groups from three drill cores (S2, S3, and S4). The S2 and S3 drill cores cover the El Mreiti Group, taken from the El Hank and Khatt areas, respectively, while the S4 drill core samples the stratigraphically correlated Atar Group taken from the Adrar area (Fig. 1C and D). Whole-rock geochemical analyses of major and trace elements, including rare earth elements, were performed at service d'analyse des roches et des minéraux (SARM) of the centre des recherches pétrographiques et géochemiques (CRPG), Nancy, France using their internal protocols (Carignan et al., 2001).

Approximately 200mg of powdered sample was fused with lithium metaborate (LiBO₂) and dissolved in nitric acid. Major element contents were measured by inductively coupled plasma atomic emission spectrometry (ICP-OES Icp 6500 radial, Thermo-Scientific),
while trace element concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS Icap-Q, Thermo-Scientific), except for Sc (ICP-OES Icp 6500 radial, Thermo-Scientific). The uncertainties refer to relative standard deviation (RSD) and are measured based on analysis of standards (see Mermet et al., 2012; Carignan et al., 2001).
Major elements such SiO₂, Al₂O₃, Fe₂O₃, and CaO with contents >10 wt.% have an uncertainties of <2 RSD. Indeed, major elements with contents >1 wt.% have uncertainties of <5 RSD for MnO and P₂O₅, uncertainties of <10 RSD for Fe₂O₃, MgO, Na₂O, K₂O and TiO₂, and <15 RSD for Al₂O₃. The loss on ignition (LOI; wt.%) values were determined following the mass difference of rock powder and separate aliquot before and after heating the replicates for 3 h at 980°C. The trace elements with concentrations >1ppm have uncertainties measured on standards (Carignan et al., 2001; Mermet et al., 2012) of <5 RSD for Eu and Er, and <10 RSD for Cr, Hf, Ta, Th, Lu, Tm, Ho, Dy, and Gd. However, uncertainties of <15 RSD for Sc, V, Y, Yb, Tb, Sm, Ce, La. The samples with concentrations of Nd and Zr >10ppm have uncertainties of <15RSD. The detection limit (D.L.) of the major elements is 0.05 wt.% for SiO₂, 0.04 wt.% for Al₂O₃, and 0.015 for Fe₂O₃ and MnO. MgO, CaO and K₂O have a detection limit of 0.03 wt.%, while 0.02% for Na₂O and TiO₂ (see appendix table A.1).
trace elements such as Nd have a detection limit of 0.016ppm, Sm (0.005ppm), Th (0.015ppm), Sc (0.6ppm), and 1.5ppm for Zr (see appendix tables A.2 and A.3).

We selected fifteen representative samples from the S2 and S4 drill cores to conduct whole-rock Sm-Nd isotope analysis on the Finnigan MAT-262 mass spectrometer at the GeOHeLis analytical facility (Géosciences Rennes/OSUR, University of Rennes, France).
The samples were spiked with a ¹⁴⁹Sm-¹⁵⁰Nd mixed solution and dissolved in a 2:1 acid mixture of 23 mol/L HF and 15 mol/L HNO₃. All the samples were dried and digested in 6 mol/L HCl. The unknowns were analyzed together with the Ames Nd-1 Nd standard and yielded average ¹⁴³Nd/¹⁴⁴Nd values of 0.511952 ± 5 in this study. The data for the unknowns
have been adjusted to the long-term ¹⁴³Nd/¹⁴⁴Nd value of 0.511963 for Ames Nd-1.
Instrumental mass fractionation was monitored and corrected using the ¹⁴⁶Nd/¹⁴⁴Nd value of
0.7219. Procedural blank analyses yielded 50 pg for Nd, and the blank is therefore considered
to be negligible. The initial Nd isotope composition (ε<sub>Nd(t)</sub> =
[((¹⁴³Nd/¹⁴⁴Nd<sub>sample</sub>/¹⁴³Nd/¹⁴⁴Nd<sub>CHUR</sub>)<sub>t</sub> - 1) * 10<sup>-4</sup>], CHUR: Chondritic Uniform Reservoir),
depleted mantle model ages (T<sub>DM</sub> = (1/λ) * ln [(¹⁴³Nd/¹⁴⁴Nd<sub>sample</sub> -
¹⁴³Nd/¹⁴⁴Nd<sub>DM(0)</sub>)/(¹⁴⁷Nd/¹⁴⁴Nd<sub>sample</sub> - ¹⁴⁷Nd/¹⁴⁴Nd<sub>DM(0)</sub> + 1) * 10<sup>-9</sup>)], and fractional deviation
of ¹⁴⁷Sm/¹⁴⁴Nd from that of chondritic meteorites (f<sup>Sm/Nd</sup> =
(¹⁴⁷Sm/¹⁴⁴Nd)<sub>sample</sub>/(¹⁴⁷Sm/¹⁴⁴Nd)<sub>CHUR</sub> - 1); McLennan et al., 1993; McLennan and Hemming,
1992) were calculated assuming present-day ¹⁴³Nd/¹⁴⁴Nd<sub>CHUR(0)</sub> = 0.512636,
¹⁴⁷Nd/¹⁴⁴Nd<sub>CHUR(0)</sub> = 0.1967, ¹⁴³Nd/¹⁴⁴Nd<sub>DM(0)</sub> = 0.51235, and ¹⁴⁷Nd/¹⁴⁴Nd<sub>DM(0)</sub> = 0.217, and a
decay constant (λ) of 6.54 × 10<sup>-12</sup> y<sup>-1</sup> (DePaolo and Wasserburg, 1976; McLennan and
Hemming, 1992). The initial ¹⁴³Nd/¹⁴⁴Nd, ε<sub>Nd(t)</sub> values, and T<sub>DM</sub> ages for the Atar and El
Mreiti sediments were calculated using the depositional age of t = 1.1 Ga based on data from
Rooney et al., (2010).

261 **4. Results**

262 **4.1. Major element concentrations**

The major element concentrations for the studied samples are presented in Table A.1
(see Appendix). The majority of the samples fall within the shale field with the exception of a
few that fall within the Fe-shale and wacke fields based on the geochemical classification
scheme of Herron (1988) (Fig. 2). Compared to the Late Archean Upper Continental Crust
(LAUCC; Condie, 1993), many Atar samples from the S4 drill core are slightly to moderately
enriched in Fe₂O₃, K₂O, Al₂O₃, and TiO₂ but depleted in SiO₂, MgO, Na₂O, and CaO (Fig.
A.1). The exceptions are samples from the Oued Tarioufet Formation (Fig. A.1A), which are
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instead enriched in CaO and MnO but depleted in other major elements, suggesting a unit
dominated by carbonates (Fig. A.1A).

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The samples from the S2 and S3 drill cores all show varying depletions and enrichments for major elements relative to LAUCC (Fig. A.1B). The samples from the En Nesoar and Touirist formations yield variable CaO and MnO contents and slight to moderate enrichments and depletions in TiO₂, Al₂O₃, K₂O, and Fe₂O₃ (Fig. A.1B; Ghnahalla et al., 2022). Most S2 samples from the Aguelt el Mabha Formation are moderately enriched in Fe₂O₃, K₂O, and TiO₂ compared to those from the Oued Tarioufet Formation (Fig. A.1). The S3 samples from the Aguelt el Mabha in the Tourine area show variable major elemental patterns with high MnO and MgO contents, reflecting considerable carbonate contents, compared to the S2 samples of the Aguelt le Mabha (Fig. A.1). Values for P₂O₅ are below the detection limit for all the samples except for two from the El Mreiti Group showing slight enrichment (Table A.1 and Fig. A.1).

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## 4.2. Trace and rare earth element concentrations

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The trace and REE concentrations are presented in Tables A.2 and A.3 (see Appendix). In general, the LAUCC-normalized trace element patterns of the Atar and El Mreiti samples are mostly similar (Fig. 3A-C). Strontium is depleted in all samples, which is likely controlled by the substitution of Ca in the plagioclase, except in two samples with elevated CaO contents. The large-ion lithophile elements (LILEs) such as Rb and Ba show variable contents. Barium is mostly depleted, and Rb is enriched in most samples. The transitional trace elements (TTEs: Cr, Sc, Ni, and V) show variable enrichments and depletions. For most samples, Cr and Sc are moderately enriched except for those from the Oued Tarioufet Formation where they are mostly depleted. Slight enrichment of V and Ni is observed on most samples from the Ksar Torchane and Tod formations, with higher
concentrations in the En Nesoar and Touirist formations of the El Mreiti Group (Fig. 3B). The concentrations of the high-field strength elements (HFSEs - Hf, Nb, Ta, Th, Y, and Zr) are variable and independent of lithology. All the samples are depleted in Hf and Y, with the exception of a few from the Foum Chor Formation with the highest observed values. Niobium, Ta, and Th are relatively enriched in most samples, whereas Zr is enriched within the fine-grained sandstone of the Foum Chor Formation due to its preferential enrichment in zircons during transport (Fig. 3A).

The patterns of the chondrite-normalized REEs show similar features compared to those of the chondrite-normalized LAUCC (Fig. 3; McDonough and Sun, 1995), which display significant light-REE (LREE) enrichment (La/N/Yb_N), fairly flat heavy-REE (HREE, Gd_N/Yb_N), and negative Eu anomalies (Eu/Eu*). The El Mreiti samples are characterized by La/N/Yb_N ratios with a range of 5.64 to 18.24 (average = 11.06), Gd_N/Yb_N ratios with a range of 1.04 to 2.46 (average = 1.64), and Eu/Eu* values ranging from 0.58 to 0.71 (average = 0.64). The Atar samples show higher values of La/N/Yb_N ranging from 9.25 to 20.38 (average = 14.56), Gd_N/Yb_N ratios ranging from 1.41 to 2.64 (average = 1.76), and Eu/Eu* values with a range of 0.65 to 0.76 (average = 0.72) (Fig. 3, Table A.3). In addition, REEs concentrations in the sediments from the Oued Tarioufet Formation are significantly lower than those from other formations due to their moderate contents of carbonates.

### 4.3. Sm-Nd isotopes

The whole-rock Sm-Nd isotope compositions of the analyzed samples are presented in Table 1. The isotope values are variable and do not show a significant relationship with lithology (Table 1). The initial <sup>143</sup>Nd/<sup>144</sup>Nd ratios range from 0.511199 to 0.511395 (average = 0.511309) for all the Atar samples and from 0.511195 to 0.511832 (average = 0.511491) for the El Mreiti samples. The <sup>147</sup>Sm/<sup>144</sup>Nd ratios range from 0.095576 to 0.1133357 (average = 0.100760) and from 0.088701 to 0.114443 (average = 0.102192) for the Atar and El Mreiti samples.
320

sediments, respectively (Table 1). All the Atar samples have negative $\varepsilon_{Nd(t)}$ values ranging from -14.18 to -11.18, T<sub>DM</sub> ages of 1.28 to 1.47 Ga, and $f^{Sm/Nd}$ from -0.5141 to -0.4237 (Table 1). In contrast, apart from one outlier sample (S2-107), the El Mreiti samples have positive $\varepsilon_{Nd(t)}$ values ranging from 2.08 to 12.00, T<sub>DM</sub> ages from 0.77 to 1.37 Ga, and $f^{Sm/Nd}$ from -0.5491 to -0.4182 (Table 1).

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# 5. Discussion

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## 5.1. Sediment maturity and hydraulic sorting

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Grain size and nature of the materials deposited in sedimentary basins are commonly controlled by hydrodynamic sorting during sediment transport, which can lead to strong heterogeneity in chemical composition, mineral differentiation, and heavy mineral enrichments (Jian et al., 2013). The chemical composition of sediments can be also influenced by the degree of sorting and maturity of sedimentary rocks. Ratios of SiO₂/Al₂O₃ are commonly used to evaluate the chemical maturity of sedimentary rocks, with elevated ratios reflecting high sediment maturity (Bankole et al., 2020; Lewin et al., 2018). As expected, all our samples are characterized by relatively low SiO₂/Al₂O₃ ratios (Fig. 2), indicating low textural maturity of the sediments.

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In addition, Th/Sc and Zr/Sc ratios can reflect heavy mineral enrichment and sediment recycling during sorting (McLennan et al., 1993). Incompatible Th and Zr elements are more enriched in felsic rocks, while compatible Sc is more enriched in mafic rocks, both preserving provenance signatures, while Zr is mainly enriched in detrital zircon (McLennan et al., 1993; Large et al., 2018). The sediments from the Atar Group exhibit slightly higher Th/Sc ratios (0.76 to 1.41, average = 1.04±0.15 σ (one std)) compared to those from sediments of the El Mreiti Group (0.63 to 1.39, average = 0.92±0.17 σ), suggesting higher contributions of felsic source rocks for the former (Fig.4, Table A.2). The samples mostly fall along the trend of
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compositional variation on the plot of Th/Sc versus Zr/Sc, with average Th/Sc ratios close to
the LAUCC (Fig. 4). The Zr/Sc ratios show significant variations, but most samples do not
show any considerable enrichments in zircons, suggesting limited roles for sediment
recycling, hydraulic sorting, and heavy minerals accumulations (Fig. 4, McLennan et al.,
1993). In addition, for all our samples, strong positive correlations of Al₂O₃ with Th and Sc
(Fig. 5A and B) suggest that the detrital phyllosilicate minerals are the predominant host
phases. Moreover, a moderate positive correlation between Al₂O₃ and Zr (Fig. 5C) also
supports limited hydraulic sorting and muted heavy mineral enrichments for our sediments.

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## 5.2. Paleoweathering intensity

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The chemical index of alteration (CIA) has been used widely to quantify the degree of weathering of source areas, where CIA = [Al₂O₃/(Al₂O₃ + CaO* +Na₂O + K₂O)] × 100 in molar proportions, and CaO* represents CaO contents associated with silicate phases (Nesbitt and Young, 1982). We correct the CaO values by eliminating the proportions from apatite and carbonate phases (e.g., McLennan et al., 1993). First, we calculated CaO' (CaO' = CaO - 10/3 × P₂O₅) to remove CaO contributions from apatite. Next, to correct for the carbonate fraction, we assumed moles of silicate CaO* = Na₂O for samples with CaO' > Na₂O, but we use the CaO' values for samples with CaO' ≤ Na₂O (Jian et al., 2013). Previous studies showed that unweathered igneous rocks are characterized by CIA values of ≤50, which increase to 60-80 for moderately weathered rocks and are greater than 80 for highly weathered rocks associated with the production of residual clays (Fedo et al., 1995; Nesbitt and Young, 1984, 1982).

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For the sediments from the Atar Group, CIA values range from 66.61 to 80.11 (average = 73.26), with the lowest values from the Tarioufet Formation (Fig. 6, Table A.1).
The CIA values for samples from the El Mreiti Group are similar to those from the Atar Group, varying from 62.86 to 80.98 (average = 72.32). Importantly, CIA values can be

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compromised by the addition of potassium ions ($K^+$) during post-depositional diagenetic (illitization) and metamorphic (metasomatism) processes (e.g., Fedo et al., 1995). The degree of chemical weathering and K-addition are commonly discernable on the $Al_2O_3$-(CaO* + Na₂O)-K₂O (A-CN-K) ternary diagram (Fig. 6; Fedo et al., 1995; Nesbitt and Young, 1984).

Most sediments from the Atar and El Mreiti groups are plotted along the A-CN axis parallel to the weathering trend of trondhjemite-tonalite-granodiorite (TTG) and for granite without any significant deviation along the A-K axis (Fig. 6), indicating a low-moderate extent of chemical weathering and limited post-depositional K-enrichment. Therefore, the range and average CIA values in the Atar and the El Mreiti samples are similar to values typical of UCC shales (70-75; McLennan et al., 1993), indicating moderate weathering of the source rocks for the sediments from the Atar and El Mreiti groups (Fedo et al., 1995; Nesbitt and Young, 1982).

We also calculated the plagioclase index of alteration — PIA = [(Al₂O₃ - K₂O)/(Al₂O₃ + CaO* + Na₂O - K₂O)] × 100 (Fedo et al., 1995) — and the chemical index of weathering — CIW = [(Al₂O₃)/(Al₂O₃ + CaO* + Na₂O)] × 100 (Harnois, 1988) — to further constrain the paleoweathering conditions of the source areas. The ranges of the PIA and CIW values of the samples from the Atar (PIA = 73.76-92.96, average = 84.96; CIW = 78.42-92.20, average = 87.89) and El Mreiti (PIA = 71.52-93.21, average = 82.12; CIW = 77.15-94.33, average = 85.52) groups are consistent with moderate chemical weathering as also indicated by the CIA proxy.
390 Concentrations of certain least-mobile incompatible trace elements (e.g., HFSEs,
391 REEs, and Th) in sedimentary rocks have been used widely to constrain the characteristics of
392 primary source rocks because they are preferentially partitioned into melts during
393 crystallization and less fractionated during sedimentary processes (e.g., Condie, 1993; Taylor
394 and McLennan, 1985). These elements are more enriched in felsic rocks compared to
395 compatible elements (e.g., Sc, Co, Cr, and V), which are more abundant in mantle-derived
396 mafic and ultramafic rocks (Large et al., 2018; McLennan et al., 1993). In our sediments, the
397 varying depletions and enrichments of the trace elements relative to LAUCC reflect the
398 varying degrees of mixing of source materials (Fig. 3). Our samples fall predominantly in the
399 felsic field, clustering around LAUCC and TTG on the compositional discriminant diagrams
400 of Th/Cr versus La/Cr and Th/Sc versus La/Sc (Fig. 7A and B; Bhatia & Crook, 1986).
401 Significantly higher Th/Sc (0.80-1.41, average = 1.04), La/Sc (2.51-4.04, average = 3.12), and
402 La/Cr (0.31-1.72, average = 0.47) from Atar Group compared to these ratios in LAUCC
403 (Th/Sc = 0.77; La/Sc = 2.5; La/Cr = 0.10; Condie, 1993) (Fig. 7A and B) indicate major
404 contributions from felsic source rocks. However, considerably lower Th/Sc, La/Sc, and Th/Cr
405 ratios in the samples from the El Mreiti Group suggest greater contributions of intermediate
406 and/or mafic components. This argument is supported by low La/Th ratios and variable Hf
407 concentrations for the Atar samples, which plot within the felsic arc field, while the El Mreiti
408 samples fall mostly in the zone between felsic and mafic sources (Fig. 7C, Floyd and
409 Leveridge, 1987).

410 REE distributions and the Eu anomaly specifically have also been used to trace the
411 provenance of siliciclastic sedimentary rocks (Bankole et al., 2020; McLennan et al., 1993).
For example, the degree of LREE enrichment over HREE can provide insights into the relative contributions of felsic and mafic components, while the size of Eu anomaly can elucidate the intracrystal differentiation of magma (Taylor and McLennan, 1985). A lack of correlation between ΣREE and Zr (Fig. 5E) and a strong positive correlation between ΣREE and Al₂O₃/K₂O (Fig. 5D and F) are taken to demonstrate that the REEs are controlled mainly by the aluminosilicate (e.g., clay) minerals (Bankole et al., 2020). Parallel chondrite normalized REE patterns, slight enrichments in the LREE over HREE (La/N/Yb_N), and significant negative Eu anomalies suggest that the Atar and El Mreiti rocks are derived, in general sense, from moderately differentiated felsic igneous rocks (Taylor and McLennan, 1985; Cullers, 1994).

### 5.3.2. Sm-Nd isotopic compositions

We used the Sm-Nd isotope systematics as an independent proxy to trace the provenance and crustal ages of our sediments (Bankole et al., 2020; Jahn and Condie, 1995; McLennan et al., 1993). While there are suggestions that some REEs may be substantially fractionated and modified during early diagenesis and/or low-grade metamorphism and/or weathering (Mathieu et al., 2001; Ohr et al., 1994), Sm and Nd are generally immobile and not fractionated, leaving whole-rock Sm-Nd isotope compositions undisturbed during sedimentary and low-metamorphic processes (DePaolo and Wasserburg, 1976; McLennan and Hemming, 1992). Sediments with typically low ¹⁴³Nd/¹⁴⁴Nd and Sm/Nd ratios, negative εNd(t) values, and high Th/Sc ratios are generally interpreted to be derived from differentiated old sources and upper continental crust in passive margin/cratonic settings. However, sediments from juvenile and mafic sources in active tectonic settings are commonly characterized by high ¹⁴³Nd/¹⁴⁴Nd ratios, positive εNd(t) values, variable but mostly high
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Sm/Nd ratios, and low Th/Sc ratios (DePaolo and Wasserburg, 1976; McLennan and Hemming, 1992).

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The invariably low ¹⁴³Nd/¹⁴⁴Nd and Sm/Nd ratios, negative εₙ₉(t), low fSm/Nd values, and high Th/Sc ratios (Table 1; Fig. 8A) of the Atar samples suggest dominant contributions from older felsic continental crust source rocks. The Atar rocks have TDM model ages from 2.27 to 2.57 Ga, with an average of 2.41 Ga (Table A.4, Fig. 8), indicating that they were dominantly derived from the older Archean crystalline basement rocks with probable mixing of Paleoproterozoic rocks from the Reguibat Shield. The Reguibat Shield is dominated by Archean gneisses and granitic rocks (2.90 – 3.25 Ga) in the western part of the terrane (Potrel et al., 1998), while the eastern part of the Shield consists mainly of Paleoproterozoic (Birimian, 2.5 – 2.0 Ga) granitic, basaltic, and metasedimentary rocks (Abouchami et al., 1990; Boher et al., 1992). Therefore, the distinctly negative εₙ₉(t) values of the Atar sediments are consistent with the dominant contribution from the granitic source rocks (Fig. 8). In contrast, the higher ¹⁴³Nd/¹⁴⁴Nd, Sm/Nd ratios, fSm/Nd values, distinctly positive εₙ₉(t), and relatively lower Th/Sc ratios (Table 1; Fig. 8) for the El Mreiti Group suggest an overwhelming contribution from juvenile and less differentiated, depleted mantle rocks (Table 1; Fig. 8). The lower TDM ages (1.95 – 2.31 Ga, average = 2.19 Ga) of the El Mreiti sediments suggest that they are sourced predominantly from the less differentiated mafic to intermediate Paleoproterozoic basement rocks of the eastern terrane of the Reguibat Shield (Fig. 8A).

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We applied Nd isotopes to model the relative contributions of the underlying Archean and Paleoproterozoic crystalline rocks to the source materials of the Atar and El Mreiti stratigraphic successions. According to the mixing model proposed by DePaolo et al. (1991), the relative involvement of the Archean crustal (AC) material can be specified by AC = (1 - α<sub>VA</sub>)*100, where α<sub>VA</sub> refers to the contribution of the arc material (= β*/[(ε<sub>Nd</sub>VA - ε<sub>NdS</sub>)/(ε<sub>NdS</sub> - ε<sub>NdAC</sub>) + β*]). β* represents the ratio of the Nd concentration in the volcanic
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arc to that of the Archean crustal rocks (Nd<sub>VA</sub>/Nd<sub>AC</sub>), ε<sub>NdVA</sub> is the isotope composition of the volcanic arc rocks, ε<sub>NdS</sub> is the isotope composition of the analyzed sediment, and ε<sub>NdAC</sub> is the isotope composition of the Archean crustal material. ε<sub>NdVA</sub> and ε<sub>NdAC</sub> were re-calculated to the constrained depositional age (t = 1.1 Ga) of the deposits (Rooney et al., 2010). The average compositions of the post-granulite granite of Touijenjert from the Amsaga complex show ε<sub>NdAC</sub> (t) = -6.37 and Nd<sub>AC</sub> = 78.38 ppm (Potrel et al., 1998), and the Tsalabia volcanite yields a ε<sub>NdVA</sub> (t) = 6.43 and Nd<sub>VA</sub> = 43.17 ppm (Boher et al., 1992), in the Char and El Mreiti areas, respectively, which were used as the end-members of the Archean and volcanic arc rocks.

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Our mixing model (Table 2) suggests a significant difference in terms of the origin for the El Mreiti and Atar sediments. The Atar materials are composed of 82.74 to 86.93 % (average = 85.06) felsic Archean rocks with much less juvenile arc materials (13 to 18%), suggesting that they are mainly sourced from the surrounding Archean crystalline basement. In contrast, the El Mreiti sedimentary inputs were dominated by relatively younger volcanic materials of the Paleoproterozoic age, with contributions ranging from 82.83 to 93.86 % (average = 86.35). It is worth noting that, although the source components of the Atar Group remain almost unchanged with stratigraphic depth, an up-section increasing trend can be observed for contributions to the El Mreiti Group from Paleoproterozoic volcanic materials. Specifically, in the basal En Nesoar Formation, the relative contribution from volcanic rocks decreases to 32 % (Table 2). In other words, this pattern clearly shows that the role played by Archean source materials became increasingly less important over time. This inference suggests that the dominant sources of Atar sediments may be considerably older than those of the El Mreiti Group, consistent with an older average model T<sub>DM</sub> age of 2.4 Ga for the Atar sediments compared to 2.19 Ga for the El Mreiti sediments. The latter is consistent with the age of the Birimian terrane. However, the age of the Atar sediments is slightly younger than
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the potential parent rocks still preserved in the Reguibat shield, which suggests the lesser
contributions from the crystalline juvenile Paleoproterozoic rocks.

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### 5.4. Implications for the tectonic-sedimentary evolution of Taoudeni Basin

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Evolution of sedimentary basins is commonly linked to the paleogeography and tectonic regimes of their source regions. Previous studies used microfossils, lithofacies, and chemo-stratigraphic correlations to suggest that the El Mreiti Group in the Khatt and Hank regions is stratigraphical equivalent to the Atar Group in the Adrar region within the Taoudeni Basin (Beghin et al., 2017b; Bertrand-Sarfati et al., 1991; Kah et al., 2012). However, our data show that the El Mreiti and Atar sedimentary rocks yield remarkably different Nd isotope compositions with overlapping T<sub>DM</sub> ages (Fig. 8). Although the two groups may show similar lithofacies and <sup>13</sup>C isotope compositions (Gilleaudeau and Kah, 2013; Kah et al., 2012), the significant older T<sub>DM</sub> ages with distinct Nd-isotope composition of the Atar Group sedimentary rocks demonstrate that they are dominantly derived from different source rock compared to the El Mreiti Group sedimentary rocks. We, therefore, infer that the stratigraphic equivalent Atar Group and El Mreiti Group sedimentary rocks, separated by a distance of ~1000 km and with overlapping isotope composition and T<sub>DM</sub> ages, have distinct sediment sources. Thus, our data reinforce the importance of sediment provenance in understanding the evolution and reconstruction of modern and ancient sedimentary systems.

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Furthermore, the considerable contributions of intermediate to mafic juvenile arc materials in the El Mreiti Group sedimentary rocks suggest their dominant parent materials were tied to a major event of mafic magmatism that affected the Eastern Reguibat shield during the Eburnean orogeny during the Paleoproterozoic at ~2.1 Ga (Abouchami et al., 1990). The Eburnean orogeny was characterized by multiple phases of crustal thickening and metamorphism of the Archean remnants and emplacement of granitic rocks at c. 2.1–2.0 Ga (Lahondère et al., 2003; Schofield et al., 2006). Traces of this orogenic event are preserved in
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the studied sections with all the El Mreiti and Atar Group sedimentary rocks plotting within
the active continental island arc field on La–Th–Sc and Th-Sc-Zr/10 discriminant diagrams
(511
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1992; Nagarajan et al., 2017).

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**6. Conclusions**

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Our geochemical data demonstrate that the fine-grained sediments from the Mesoproterozoic Atar and El Mreiti groups are texturally immature with limited sediment recycling. Relatively low CIA values suggest that the source rocks of our sediments experienced only moderate weathering with muted post-depositional addition of K+ ions. In other words, their geochemical signatures were not considerably overprinted by sedimentary processes. Therefore, they can be used to trace the provenance of the source materials. The signatures of the relatively immobile trace elements suggest likely sediment mixing of different sources with a dominance of felsic source rocks, while contributions from the mafic components are relatively minor for our sediments. Specifically, the El Mreiti Group sediments display greater contributions of mafic and intermediate components compared to the Atar Group sediments.

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The Sm/Nd isotope systematics suggest that the Atar Group sedimentary rocks were dominantly derived from mixing of moderately differentiated Archean felsic source rocks with a minor contribution from younger Paleoproterozoic intermediate to mafic arc materials of the Reguibat shield. In contrast, the El Mreiti Group sediments were significantly sourced from the juvenile Paleoproterozoic terrane that are linked to the emplacement of mafic magmatic events during the Eburnean orogeny. Our mixing model and T<sub>DM</sub> age calculation demonstrate that the source rocks of the Atar sediments were substantially older than those of the El Mreiti samples, consistent with the dominant juvenile model age and temporally
varying contribution of juvenile volcanic arc contribution to the El Mreiti Group samples. We infer a distinctive Nd-isotopic geochemical character for these sediments related to their different parent rocks. This study employs a comprehensive source-to-sink approach to the rocks of the Atar and El Mreiti groups. The value of our methods in this study suggests similar potential in efforts to unravel source control and sedimentary-tectonic evolution for other ancient sedimentary basins.

## Acknowledgments

Funding was provided by the Region Nouvelle Aquitaine, French Embassy at Nouakchott (Mauritania), and Interdisciplinary Consortia for Astrobiology Research (ICAR) within NASA's Astrobiology Program (T.W.L.). They are acknowledged for their support and collaboration. The authors are also grateful to the Ministry of Petroleum, Mines, and Energy of Mauritania and TotalEnergies for their assistance and sample processing. We thank C. Lebailly, E. Marcon, A. Meunier, C. Laforest, A. Hourmatallah, E. M. Ehmeida, J-P. Girard, G. Graffin, and J-A. Dal for their assistance and support.

## Figure captions

**Fig. 1.** A) Map of Africa indicating the location of Mauritania (inset rectangle). B) Geological map showing the distribution of crystalline basements rocks and sedimentary successions of the Taoudeni Basin across the West African Craton (modified after Deynoux and others, 2006). C) Regional geological map of the studied area showing the locations of the studied drill cores (modified after Moussine-Pouchkine and Bertrand-Sarfati, 1997). D) Generalized lithostratigraphic column of the studied El Mreiti (S2 and S3) and Atar (S4) drill cores. The Re-Os geochronology data are from Rooney et al. (2010).

**Fig. 2.** Plot of the Atar and El Mreiti group sediments on the geochemical classification diagram of Herron (1988).

**Fig. 3.** Trace element diagrams for A) Atar Group, B) and C) El Mreiti Group in S2 and S3 drill cores, respectively. The data are normalized to the composition of the Late Archean Upper Continental Crust (LAUCC)
559 from Condie (1993). Chondrite-normalized Rare Earth Element patterns for D) Atar Group, E) and F) El Mreiti Group in S2 and S3 drill cores, respectively. The data are compared with the LAUCC (from Condie, 1993) and chondrite values are from (McDonough and Sun, 1995).

562 **Fig. 4.** Plot of Th/Sc vs Zr/Sc for the Atar and El Mreiti groups sediments (after McLennan et al., 1993). Data for LAUCC, basalt, granite, and TTG (tonalite-trondhjemite-granodiorite) are from Condie (1993).

564 **Fig. 5.** Plot of A-B-C-D) Th, Sc Zr, and ΣREE versus Al₂O₃, respectively. E) ΣREE versus Zr, and F) ΣREE versus K₂O.

566 **Fig. 6.** A–CN–K (Al₂O₃–CaO + Na₂O–K₂O) ternary diagram for the Atar and El Mreiti group sediments (after Nesbitt and Young, 1984). Arrows 1, 2, and 3 indicate potential weathering trends for basalt, TTG, and granite, respectively. Data for basalt, TTG, and granite are from Condie (1993). CIA: chemical index of weathering.

569 **Fig. 7.** Source-rock trace element discriminant diagrams of A) plot of Th/Cr vs La/Cr, B) Th/Sc vs La/Sc (after Bhatia and Crook, 1986), and C) La/Th vs Hf after (Floyd and Leveridge, 1987) for the Atar and El Mreiti sediments. For comparison, the main potential sources are also plotted. Data for LAUCC, granite, TTG, and basalt, are from Condie (1993).

573 **Fig. 8.** Plots of A) fSm/Nd versus εNd(t) (after McLennan et al., 1993) illustrate the Sm-Nd isotope systematics. Data for the LAUCC, MORB, and Arc rocks are from Taylor and McLennan (1985). B) Average TDM age versus εNd(t) plot for the Atar and El Mreiti group sediments compared with those of potential sources rock in the Reguibat Shield. εNd values were calculated at t = 1.1 Ga. Data for the Reguibat rocks are (after Abouchami et al., 1990; Boher et al., 1992; Potrel et al., 1998; Schofield et al., 2012; Key et al., 2008).

578 **Fig. 9.** A) Ternary diagrams La-Th-Sc, and B) Th-Sc-Zr/10 of trace elements tectonic discrimination for the studied sediments (after (Bhatia and Crook, 1986). ACM: Active Continental Margin, PM: Passive Margin, CIA: Continental Island Arc, and OIA: Oceanic Island Arc.

581 **Table captions**

582 **Table 1.** Sm-Nd whole-rock isotope data for the Atar (S4 drill core) and El Mreiti (S2 drill core) sediments. εNd(t) values were calculated at t = 1.1 Ga.

584 **Table 2.** Modeled fractions of compositionally different Archean crust and volcanic arc in the analyzed sediments of the Atar and El Mreiti groups.
586

587 **Figure appendix captions**

588 **Fig. A.1.** Major element plots compared to the Late Archean Upper Continental Crust (LAUCC) from Condie (1993) for Atar Group: A) Oued Tarioufet, B) Tod, C) Ksar Torchane, and D) Foum Chor formations. El Mreiti Group-S2 drill core: E) Aguelt el Mabha, F) Touirist, and G) En Nesoar formations. El Mreiti Group-S3 drill core: H) Aguelt el Mabha.
589
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591

592 **Table Appendix Captions**

593 **Table A.1.** Bulk chemical composition of the Atar (S4 drill core) and El Mreti group (S2 and S3 drill cores) sediments. D.L.:detection limit. LOI: loss on ignition. CIA: chemical index of alteration. PIA: plagioclase index of alteration CIW: chemical index of weathering
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596 **Table A.2.** Whole-rock of selected trace elements geochemical data and Th/Sc ratios of the
597 Atar (S4 drill core) and El Mreiti group (S2 and S3 drill cores) sediments. D.L.:detection
598 limit.
599

600 **Table A.3.** Whole-rock Rare Earth Element geochemical data for the studied sediments. D.L.:detection limit. Eu anomaly, Eu/Eu*: EuN/ (0.67*SmN + 0.33*TbN), where N refers to the chondrite-normalized value. Chondrite values are from (McDonough and Sun, 1995).
601

602 **Table A.4.** The εNd(t) and TDM ages data for the Atar and El Mreiti group sediments and their potential source rocks from the Reguibat Shield. Data for the Reguibat rocks are (after Abouchami et al., 1990; Boher et al., 1992; Potrel et al., 1998; Schofield et al., 2012; Key et al., 2008).
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607
608 References

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<table><caption>Table 1. Sm-Nd whole-rock isotope data for the Atar (S4 drill core) and El Mreiti (S2 drill core) sediments. $\varepsilon_{Nd}$ (t) values were calculated at t = 1.1 Ga.</caption><thead><tr><th></th><th>Sample</th><th>Sm (ppm)</th><th>Nd (ppm)</th><th>Sm/Nd</th><th><sup>147</sup>Sm/<sup>144</sup>Nd</th><th><sup>143</sup>Nd/<sup>144</sup>Nd</th><th><sup>143</sup>Nd/<sup>144</sup>Nd (1.1 Ga)</th><th>ε<sub>Nd</sub> (0)</th><th>ε<sub>Nd</sub> (1.1 Ga)</th><th>T<sub>DM</sub> (Ga)</th><th>f<sup>Sm/Nd</sup></th></tr></thead><tbody><tr><td rowspan="8">El Mreiti</td><td>S2-023</td><td>8.02</td><td>46.22</td><td>0.173543</td><td>0.104890</td><td>0.511487</td><td>0.510732</td><td>-22.406641</td><td>5.255073</td><td>2.25</td><td>-0.466752</td></tr><tr><td>S2-032</td><td>6.04</td><td>36.35</td><td>0.166129</td><td>0.100410</td><td>0.511525</td><td>0.510801</td><td>-21.679189</td><td>5.984543</td><td>2.12</td><td>-0.489529</td></tr><tr><td>S2-056</td><td>4.87</td><td>25.73</td><td>0.189333</td><td>0.114443</td><td>0.511832</td><td>0.511007</td><td>-15.682113</td><td>11.998245</td><td>1.95</td><td>-0.418186</td></tr><tr><td>S2-078</td><td>7.45</td><td>44.17</td><td>0.168753</td><td>0.101995</td><td>0.511486</td><td>0.510751</td><td>-22.430556</td><td>5.231093</td><td>2.20</td><td>-0.481470</td></tr><tr><td>S2-084</td><td>4.04</td><td>22.58</td><td>0.179054</td><td>0.108224</td><td>0.511598</td><td>0.510818</td><td>-20.251999</td><td>7.415689</td><td>2.17</td><td>-0.449804</td></tr><tr><td>S2-103</td><td>4.56</td><td>27.09</td><td>0.168259</td><td>0.101696</td><td>0.511480</td><td>0.510748</td><td>-22.542610</td><td>5.118728</td><td>2.20</td><td>-0.482991</td></tr><tr><td>S2-107</td><td>6.43</td><td>43.78</td><td>0.146769</td><td>0.088701</td><td>0.511195</td><td>0.510555</td><td>-28.117041</td><td>-0.471157</td><td>2.31</td><td>-0.549054</td></tr><tr><td>S2-114</td><td>6.88</td><td>42.78</td><td>0.160787</td><td>0.097176</td><td>0.511325</td><td>0.510625</td><td>-25.569960</td><td>2.082985</td><td>2.31</td><td>-0.505968</td></tr><tr><td rowspan="7">Atar</td><td>S4-010</td><td>2.52</td><td>15.91</td><td>0.158179</td><td>0.095600</td><td>0.511332</td><td>0.510643</td><td>-25.439631</td><td>-11.260705</td><td>2.27</td><td>-0.513979</td></tr><tr><td>S4-020</td><td>1.91</td><td>10.91</td><td>0.175261</td><td>0.105925</td><td>0.511356</td><td>0.510593</td><td>-24.970162</td><td>-12.245111</td><td>2.45</td><td>-0.461490</td></tr><tr><td>S4-063</td><td>7.25</td><td>44.81</td><td>0.161892</td><td>0.097841</td><td>0.511199</td><td>0.510494</td><td>-28.031168</td><td>-14.175275</td><td>2.48</td><td>-0.502586</td></tr><tr><td>S4-112</td><td>7.35</td><td>45.86</td><td>0.160319</td><td>0.096892</td><td>0.511248</td><td>0.510550</td><td>-27.079696</td><td>-13.087350</td><td>2.40</td><td>-0.507413</td></tr><tr><td>S4-136</td><td>8.01</td><td>50.65</td><td>0.158141</td><td>0.095576</td><td>0.511268</td><td>0.510579</td><td>-26.691080</td><td>-12.512168</td><td>2.35</td><td>-0.514103</td></tr><tr><td>S4-171</td><td>12.36</td><td>65.93</td><td>0.187556</td><td>0.113357</td><td>0.511395</td><td>0.510578</td><td>-24.210594</td><td>-12.530954</td><td>2.57</td><td>-0.423706</td></tr><tr><td>S4-215</td><td>8.46</td><td>51.08</td><td>0.165667</td><td>0.100127</td><td>0.511369</td><td>0.510647</td><td>-24.721967</td><td>-11.178996</td><td>2.31</td><td>-0.490968</td></tr></tbody></table>
<table><caption>Table 2. Modeled fractions of compositionally different Archean crust and volcanic arc in the analyzed sediments of the Atar and El Mreiti groups.</caption><thead><tr><th></th><th>Sample</th><th>Nd (ppm)</th><th>ε<sub>Nd</sub> (1.1 Ga)</th><th>% of Archean crust</th><th>% of volcanic arc</th></tr></thead><tbody><tr><td rowspan="6">El Mreiti</td><td>S2-023</td><td>46.22</td><td>5.255073</td><td>15.50</td><td>84.50</td></tr><tr><td>S2-032</td><td>36.35</td><td>5.984543</td><td>6.14</td><td>93.86</td></tr><tr><td>S2-078</td><td>44.17</td><td>5.231093</td><td>15.80</td><td>84.20</td></tr><tr><td>S2-103</td><td>27.09</td><td>5.118728</td><td>17.17</td><td>82.83</td></tr><tr><td>S2-107</td><td>43.78</td><td>-0.471157</td><td>67.99</td><td>32.01</td></tr><tr><td>S2-114</td><td>42.78</td><td>2.082985</td><td>48.29</td><td>51.71</td></tr><tr><td rowspan="7">Atar</td><td>S4-010</td><td>15.91</td><td>-11.260705</td><td>86.79</td><td>13.21</td></tr><tr><td>S4-020</td><td>10.91</td><td>-12.245111</td><td>85.23</td><td>14.77</td></tr><tr><td>S4-063</td><td>44.81</td><td>-14.175275</td><td>82.74</td><td>17.26</td></tr><tr><td>S4-112</td><td>45.86</td><td>-13.087350</td><td>84.06</td><td>15.94</td></tr><tr><td>S4-136</td><td>50.65</td><td>-12.512168</td><td>84.85</td><td>15.15</td></tr><tr><td>S4-171</td><td>65.93</td><td>-12.530954</td><td>84.82</td><td>15.18</td></tr><tr><td>S4-215</td><td>51.08</td><td>-11.178996</td><td>86.93</td><td>13.07</td></tr></tbody></table>