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Paleogeography of the Eosahabi River in Libya: New insightsinto the mineralogy, geochemistry and paleontology of Member U1of the Sahabi Formation, northeastern Libya

A.M. Muftah a,b, P. Pavlakis a,c, A. Godelitsas a,⇑, P. Gamaletsos a,d, N. Boaz c,e

a University of Athens, Faculty of Geology and Geoenvironment, Panepistimioupolis, Zographou 15784, Athens, Greeceb Benghazi University, Faculty of Science, Department of Earth Sciences, Benghazi, Libyac International Institute for Human Evolutionary Research, Integrative Centers for Science and Medicine, 12 Starling Avenue, Martinsville, VA 24112, USAd Karlsruhe Institute of Technology, Institute for Photon Science and Synchrotron Radiation, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germanye Virginia Commonwealth University, Richmond, VA 23284, USA

a r t i c l e i n f o

Article history:Received 22 June 2011Received in revised form 25 September2012Accepted 28 September 2012Available online 26 October 2012

Keywords:SahabiLibyaSedimentsClaysGeochemistry

a b s t r a c t

A large paleo-river of Miocene age traversing Libya from south to north has been previously demon-strated by seismic, stratigraphic, paleontological, and remote sensing data. The depositional environmentof As Sahabi Formation in north central Libya is this large and now extinct Eosahabi River. However, thesource of this major African river has remained controversial. Dark-colored sedimentary material withmagnetic properties suggested a source from the basaltic Haruj as Aswad massif in south central Libya.To test this hypothesis, mineralogical and geochemical study of clayey sediments from three localities,P25, P28 and P96c, from fossiliferous Member U1 of the As Sahabi Formation, were carried out. Resultsstrongly indicate very mature and re-processed sediments of continental origin, and felsic sources withno basaltic contribution. Thus the origin can be traced to an upland area of outcrop of rocks of Precam-brian continental origin in northeastern Chad. An alternative scenario is that the Sahabi sediments orig-inated from Precambrian outcrops in Ethiopia through an east–west river connection with the Nile. Weconsider this hypothesis unlikely, since it is based only on remote sensing data, and lacks any time con-trol or geological supporting evidence. The abundant vertebrate fauna from the Sahabi Formation showsstrong similarities with penecontemporaneous fossil faunas in Chad and is supportive of an origin of theEosahabi River in Neogene mega-Lake Chad.

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1. Introduction

Within the framework of the East Libya Neogene Research Pro-ject (ELNRP), the present study focused on selecting clayey sedi-ment samples from fossiliferous Member U1 of three localities(P25, P28 and P96c), located in the Sahabi area, northeastern SirtBasin (Fig. 1). The sediments were subjected to detailed mineralog-ical and geochemical investigation taking into account their pale-ontological significance.

The Sahabi Formation comprises four informal members frombottom to top – T, U, V, and Z. Within Members U and V thereare several units. Member U1 of the Sahabi Formation consists ofseveral interbedded levels of clays, sands and shell beds located be-tween two thin dolomitic horizons, considered as shore and lagoonfeatures by De Heinzelin and El-Arnauti (1983). More detailedinformation about the criteria of this stratigraphy is provided by

De Heinzelin and El-Arnauti (1983) and Muftah et al. (2008a).The Sahabi Formation was assigned a Pliocene age by De Heinzelinand El-Arnauti (1987) based on the identification of Formation P asMessinian in age. The Sahabi Formation now is assigned to LateMiocene as indicated biostratigraphically (Boaz, 2008, 2009; Boazet al., 2008). The lower two rock units exposed in the Sahabi area(Formation ‘‘M’’ and Formation ‘‘P) are dated as Late Miocene inage based on marine biostratigraphic correlation to the Mediterra-nean deep sea record (Muftah et al., 2008b).

There are no previous mineralogical and geochemical investiga-tions for the Sahabi Formation, except some notes on clay types, byDe Geyter and Stoops (in De Heinzelin and El-Arnauti, 1987), whoconcluded that the phyllosilicates are characterized by an associa-tion of smectite, kaolinite and mica in various proportions, butsmectite usually predominates. Beyer (2008) reported a stronglymagnetic bed of what he considered a re-deposited tuff in the flu-viatile facies of Member U1 at locality P28. However, the volcanicorigin of this material, related to Al Haruj basalts, has not beenconfirmed.

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⇑ Corresponding author. Tel.: +30 2107274689.E-mail address: [email protected] (A. Godelitsas).

Journal of African Earth Sciences 78 (2013) 86–96

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2. Materials and methods

The sediments studied in the present work originate in the fos-siliferous Member U-1 of the As Sahabi Formation and particularlyfrom P25, P28 and P96c localities (see Fig. 1). A total of 34 samplesfrom the P25 stratigraphic column, 13 from the P28 column, and19 from the P96c column were collected during fieldwork(Fig. 2). Eight 8 characteristic clayey sediment samples (P25-34,P25-20, P25-14, P25-10, P25-6, P25-3; P28-25; P96c-7), containingmacrofossils (vertebrate-mammals) and microfossils, were chosenfor geochemical and mineralogical characterization. Concerningmicropaleontology, all samples from all localities were processedfor foraminifera, ostracoda and calcareous nannofossils, accordingto the standard micropaleontological techniques.

Bulk Powder X-ray Diffraction (PXRD) patterns were initially re-corded for representative raw (untreated with ethylene glycol andunheated) sediment samples, from P25, P28 and P96c localities of

Member U1, using a Philips PW 1710 diffractometer with Ni-fil-tered Cu Ka radiation. Additionally, the silt + fine sand fraction(2 lm – 63 lm + 63 lm – 250 lm), as well as the clay fraction(<2 lm), separated using standard wet-chemical and centrifuga-tion procedures (Moore and Reynolds, 1997), were also investi-gated with regard to raw, glycolated and heated samples(550 �C). The SEM-EDS investigation was carried out using a JEOLJSM-5600 system equipped with an Oxford LINK EDS.

Bulk geochemical analyses for major (Si, Al, Fe, Mg, Ca, Na, K, Ti,P, Mn, Cr) and trace elements (Ba, Be, Co, Cs, Ga, Hf, Nb, Rb, Sn, Sr,Ta, Th, U, V, W, Zr, Y, REE) were performed using a Perkin ElmerICP-OES and a Perkin Elmer Sciex Elan 9000 ICP-MS, respectively,following the LiBO2/LiB4O7 fusion and HNO3 digestion of a 0.2-gsample. In addition, a separate 0.5-g split was digested in hot(95 �C) aqua regia (HNO3:HCl mixture 1:3) and analysed by ICP-MS for base and precious metals (Mo, Cu, Pb, Zn, Ni, As, Cd, Sb,Bi, Hg, Tl, Se, Ag, Au). The loss on ignition (LOI) was also measured

Fig. 1. The As Sahabi Formation at northeastern Sirt Basin (Libya, N. Africa).

A.M. Muftah et al. / Journal of African Earth Sciences 78 (2013) 86–96 87


at 1000 �C using standard procedures, as well as total S and C (TOT/S, TOT/C) using a Leco analyzer.

3. Results and discussion

3.1. Mineralogy and geochemistry with implications about the originof the sediments

The bulk PXRD patterns (Figs. 3–5) of representative raw sedi-ments from P25, P28 and P96c localities of Member U1 provedthe presence of abundant quartz (SiO2), particularly in the case ofP96c. The materials from the P96c locality contain, except feld-spars, carbonate minerals, specifically dolomite (CaMg(CO3)2)which is absent in the other localities (see SEM image of Fig. 5).On the other hand, halite (NaCl) is present only in the case ofP25 together with phyllosilicates (chlorite, illite, smectite) andminor feldspars. In this locality, quartz, halite and feldspars aremainly concentrated in the coarse material (non-silt + fine sand &-clay fraction). Silt + fine sand contain abundant chlorite as wellas illite and smectite. The identification of the latter clay mineralswas finally based on PXRD (raw, glycolated and heated at 550 �C)of the clay fraction (<2 lm). Thus it was established that the clayminerals occurring in the sedimentary materials from P25 and alsoP28 localities are mostly represented by smectites (d = 12.4 Åshifted to d = 17 Å at the glycolated sample) and minor illite(d = 10 Å not shifted at the glycolated sample). However, in thecase of P96c locality, where the sediments seem to be extremelyfelsic and rather immature (see text below), only illite is presentin the clay fraction. It should be noted that the clay fraction, ofall investigated sediments from the fossiliferous Member U1, com-prises a very small part of the samples (less than 1%).

The bulk geochemical composition of As Sahabi sediments, fromP25, P28 and P96c localities of Member U1, is presented in Table 1.It is evident that the concentration of most of the major chemicalelements (Al, Fe, Mg, K, Ti, P, Mn) is comparable to that of the

Upper Continental Crust/UCC (Rudnick and Gao, 2003). However,there is less Si (SiO2: 66.60 wt.% in UCC) except P96c locality wherethere is excess SiO2 (mostly due to quartz, see PXRD above) but lessAl2O3. The Ca content at P25 and P28 is also very low (CaO:3.59 wt.% in UCC) while it is, again, elevated in the case of P96c, to-gether with Mg and total C (due to dolomite, see PXRD above). Inthe case of P25 and P28, MgO corresponds to Mg-aluminosilicatesand specifically phyllosilicates (such as chlorites, see PXRD above).The Na content is also very low to P96c and P28 (Na2O: 3.27 wt.% inUCC), but it is apparently increased to P25 locality samples mostlydue to halite (see PXRD above). It is worthwhile to mention that allthe investigated sediments from fossiliferous Member U1 containconsiderable amounts of K, attributed most likely to K-phyllosili-cates (illite), which could be essential for potential absolute datingpurposes. However, it is complicated to carry out bulk K/Ar or evenmicro-40Ar/39Ar dating on the basis of illite because the authigen-esis of the clays has to be proved by crystallinity measurements(e.g. Dickin, 2005) using a combination of detailed XRD (study of10 Å illite reflection) and HRTEM (elucidation of polytypism). Theincomplete study of illitization reactions, which is a complicatedissue beyond the scope of the present paper, may easily lead to‘‘mixed ages’’ and wrong geochronology (e.g. Srodon et al., 2002).Regarding absolute geochronology of the Member U1 As Sahabisediments and fossils, which could be the subject of future re-search, there are also significant quantities of other suitable ele-ments (U, Be, etc.). The relatively high concentrations of Fe(Table 1), despite the absence of major Fe-minerals (see PXRDabove), can be attributed to minor phyllosilicates (mainly chlo-rites), to authigenic/diagenetic phases (e.g. Fe-oxides and/or oxy-hydroxides) and also to detrital minerals (e.g. ilmenite). It shouldbe emphasized that the As Sahabi sediments contain a variety ofdetrital minerals, such as Cr-spinels and zircons (Fig. 6), hostingboth major and trace elements.

Concerning trace elements, the samples from P25 and P28localities are exceptionally enriched in ‘‘incompatible’’ elements

Fig. 2. Stratigraphic columns, including the fossiliferous Member U1 (see also Fig. 1), at P25, P28 and P96c localities of As Sahabi Formation.

88 A.M. Muftah et al. / Journal of African Earth Sciences 78 (2013) 86–96


(particularly actinides, i.e. Th and U, HFSE and REE) and depleted incertain ‘‘compatible’’ elements (Zn, Cu, Ni, etc.) when normalisedwith the Upper Continental Crust (UCC, Rudnick and Gao, 2003),see spider diagrams in Fig. 7. The main negative anomalies concernBa, Pb, P and Sr which can be attributed mainly to relative feldspar,apatite and calcite absence in the sediments. However, Ti concen-tration is relatively high because of detrital Fe/Ti- (e.g. ilmenite)and Ti-oxides (rutile). The above minerals are indeed abundant inAl Haruj basalts, but geochemical discrimination diagrams excludesuch an origin (see text below). On the other hand, the existence ofdetrital minerals, and namely zircon (ZrSiO4, see Fig. 6), is alsoresponsible for the relatively high concentrations of Zr and rele-vant HFSE elements (mainly Hf, Th, U) as well as REE. All the above

indicate a potential contribution of a felsic, and not a mafic (orultramafic), source to the geochemical character of the sediments,which is close to UCC. Additionally, though the sediments fromP96c locality exhibit a different geochemical character, comparedto P25 and P28 (due to unusual combination of silicate and carbon-ate minerals), they still show a clear felsic affinity. This is also sup-ported by the REE patterns following the pattern of UCC,characterized by LREE enrichment and relative HREE depletion(Fig. 8). The slightly different trend of P96c sediments could be ex-plained by their enhanced immature and felsic character related toexpected zircon accumulation causing a relative HREE enrichmentand also an Yb anomaly (e.g. Grimes et al., 2007). In order to ex-clude involvement of neighbouring volcanic rocks in the Member

210 345

Bulk sediment P-25

d - Scale

Qz : quartzFsp : feldsparIlt : IlliteChl : chloriteHl : haliteSme : smectite

Sme

QzIlt

Chl

Ilt

Ilt

Fsp

FspChl

Qz

Hl

QzQzQz

310 4520

Silt fraction + Fine sand (> 2 µm)

d - Scale

Smectite

Illite

IlliteQua

rtz

Chlorite

Chlorite

Illite

P-25

310 4520

Clay fraction (< 2 µm):

Raw, Glycolated, Heated

d - Scale

Smectite

Illite

Illite

ChloriteChlorite

Illite

P-25

Fig. 3. PXRD patterns (bulk, silt fraction, and clay fraction) of composite clayeysediment sample from Member U1 of P25 locality.

210 345

Bulk sediment P-28

d - Scale

Qz : quartzFsp : feldsparIlt : IlliteChl : chloriteSme : smectite

Sme

Qz

Ilt ChlIlt

IltFsp

Chl

Qz

QzQz Qz

310 4520

Silt fraction + Fine sand (> 2 µm)

d - Scale

Smectite Illite

Illite

Qua

rtz

Chl

orite Chlorite

Illite Qua

rtz

P-28

310 4520d - Scale

Smectite

Illite

Illite

Chlorite

Chlorite

Illite

P-28Clay fraction (< 2 µm):

Raw, Glycolated, Heated

Fig. 4. PXRD patterns (bulk, silt fraction, and clay fraction) of composite clayeysediment sample from Member U1 of P28 locality.



U1 sediments, the corresponding geochemical trends of Al Harujwithin-plate alcaline basaltic rocks located in south central Libya(Farahat et al., 2006; Cvetkovic et al., 2010), and also Wan an Na-mous—Al Haruj volcanics (Bardintzeff et al., 2012), have been in-cluded in Figs. 7 and 8. The different spider diagrams andgeochemical anomalies, and more characteristically the contrast-ing Ba, P, Ti and Ni behaviour, as well as the different Eu anomalies,may indicate no influence of the entire Al Haruj volcanic massif inthe formation of As Sahabi sediments. However, only dissimilari-ties in spider diagrams and different Eu anomalies cannotundoubtedly ensure the absence of basaltic (basic) component inthe studied sediments. Thus, specific geochemical discriminationdiagrams are needed (see text below). Moreover, geochemical cal-culations, using element mobilization and fractionation duringrock weathering (e.g. Nesbitt, 1979; Soler and Lasaga, 1996), in or-der to assess the potential Al Haruj basalts contribution in theMember U1 sediments, cannot reliably be performed because ofmultiple ‘‘immobile’’ mineral (Ti-minerals, zircon, etc.) sourcesand mature (extensively re-processed) sediments.

Consequent geochemical discrimination diagrams (Floyd andLeveridge, 1987; Rollinson, 1993; Plank and Langmuir, 1998; Tot-ten et al., 2000; Johanesson and Leybourne, 2008), concerningthe possible origin (provenance) of the sediments, are presentedin Figs. 9 and 10. The felsic contribution to the UCC general charac-ter of the sediments is apparent. This result suggests, followingGriffin (2002, 2006), that acidic igneous rocks (or perhaps acidicmetamorphic rocks), such as the Precambrian granites of north-eastern Chad, supplied sediment to the As Sahabi area throughout

geological time. It is therefore argued that the mafic volcanic rocks,such as the Al Haruj basalts representing the largest volcanic prov-ince in Libya (Farahat et al., 2006; Cvetkovic et al., 2010; Bard-intzeff et al., 2012) are not the sources for the Member U1sedimentary rocks. This is also supported by the suggested geo-chemical diagram of Fig. 11, where all volcanic rocks of Libya(Bardintzeff et al., 2012) are compared to the rocks characterizedin the present study. In addition the sediments are very matureand re-processed with an old sediment component of continentalorigin probably of northeastern Chadian origin. Taking into ac-count all the above mineralogical and geochemical data, presentedfor the first time in the literature, we can suggest the potentialsource areas of the fossiliferous (Member U1) As Sahabi sedimen-tary rocks as illustrated in Fig. 12 (the geological formations of Li-bya and Chad were taken from Schlueter, 2008). Thispaleogeographic reconstruction compares well with that of theEosahabi River as outlined from remote sensing data by Griffin(2006) and Drake et al. (2008).

The suggestion that Member U1 sediments may originate ingeological formations occurring in the south or even south-eastof Libya, can also raise implications about association of As Sahabiwith the Nile River. However, that remains a theory. Carmignaniet al. (2009) suggested from remote sensing data that the ‘‘SahabiChannels’’ of Barr and Walker (1973), extended by Nicolai (2008)into the Mediterranean Basin by the use of seismic data, repre-sented a late Miocene incursion of the Nile River into Libya. Sucha model requires escape of the Nile from its basin and flow uphillover the higher relief Western Desert to enter the Ajdabya Troughand eventual entry into the Gulf of Sirt. The model is not supportedby data on Miocene paleo-relief of western Egypt that would makesuch a hypothesis plausible, and recent remote sensing data(Paillou et al., 2009) support a separate Libyan hydrographic drain-age pattern distinct from the Nile. While the composition of theSahabi Member U1 sediments might also be explained by an originfrom Precambrian outcrops within the Ethiopian Highlands nearLake Tana in the catchment area of the Blue Nile, paleontologicalevidence (see below) renders this is an unlikely hypothesis. Theconnection of As Sahabi with Nile argument so far is based on indi-cations from remote sensing data. Further investigation is requiredto determine the dating of this hypothesis, as well as insights intothe geology of Nilo-Sudan region.

3.2. Paleontology and biogeography of the Eosahabi River in the lightof the new mineralogical and geochemical data

The micropaleontological investigation of all studied samplesfrom Member U1 yielded only badly preserved benthic foraminif-era in samples 30 and 31 from P25 locality (Fig. 2). The only micro-fossils retrieved from the processed sediments of the above localitywere benthic foraminifers. The lower sample (30) is more argilla-ceous and contained common pyrite of framboidal type, probablyindicating a reducing depositional environment with sparse ofagglutinated foraminifera Haplophragmoides spp., meanwhile theupper sample (31) is of lagoonal condition as indicated by the pres-ence of common Pararotalia spp. of bad preservational state due tothe replacement by dolomite. The biostratigraphical importance ofthe Pararotalia spp. as a genus is very characteristic to the Neogene.

Sahabi preserves a wide diversity of habitats, ranging from mar-ine shelf to freshwater fluviatile. Lagoonal facies, however, are pre-dominant. For biogeographic overview of Sahabi see Munthe, 1987;Bernor and Rook, 2008 and Boaz et al., 2008, and for its paleoecol-ogy see Boaz et al., 2008 and Boaz, 2009. Abundant fossil wood doc-uments the presence of forest composed of species with exclusivelyAfrican affinities, fringing the large Eosahabi River. Fire-scarring inseveral specimens indicates the presence of fire-maintained open‘‘savanna’’ as a habitat (Deschamps, 1987). Open woodland and

210 345

Bulk sediment P96c

d - Scale

Qz : quartzFsp : feldsparIlt : IlliteDl : Dolomite

Qz

Ilt FspIlt

Ilt

FspQz

QzQzQz

Fsp

Ilt

Dl

Fsp Dl

DlQz

QzDl

Qz

Qz

Dl

Fig. 5. Upper: PXRD pattern (bulk) of composite clayey sediment sample fromMember U1 of P96c locality; the clay fraction (not shown) contains only illite.Lower: SEM image of dolomite crystals.



grassland ‘‘savanna’’ were habitats occupied by many of the ungu-late taxa. One half of the small mammal fauna was composed ofgerbils, the species Abudhabia yardangi, named from Sahabi. Gerbilsare characteristic of arid sandy habitats. The discovery of fossilsfrom the Sahabi Formation of large-sized fish of taxa known to in-habit fresh water drew attention to the presence of a large riverin the area at the time (Gaudant, 1987). The discovery of freshwaterdiatoms in a coprolite of the Sahabi Formation Member U1 indi-cated a large, slow-flowing river (Burckle, 1982). Other fauna indic-

ative of riverine habitats are hippopotamids (Gaziry, 1987; Pavlakis,2008), crocodilids (Hecht, 1987; Delfino, 2008), iniid river dolphins(Whitmore, 1987), and anthracotheres (Pavlakis and Boaz, 2008).Boaz (2008) and Boaz et al. (2008) reviewed the Sahabi fauna andposited a close paleobiogeographic connection with the similarlyaged latest Miocene Toros-Menalla fauna of northern Chad (Vig-naud et al., 2002; Viriot et al., 2008). Lihoreau et al. (2006) basedon the anthracothere Libycosaurus petrocchii, which is well docu-mented in both Toros-Menalla in Chad and in Sahabi, supported a

Table 1Major and trace element analyses of the fossiliferous Member U1 sediments at P25, P28 and P96c localities of As Sahabi Formation (see also Figs. 1 and 2).

P25-34 P25-20 P25-14 P25-10 P25-6 P25-3 P28-25 P96cwt.% wt.% wt.% wt.% wt.% wt.% wt.% wt.%

SiO2 54.8 66.31 53.2 54.35 65.18 52.22 67.2 74.68Al2O3 14.34 8.36 15.87 17.13 11.56 17.12 12.03 3.35Fe2O3 7 4.35 5.23 5.02 5.58 6.76 4.31 1.48MgO 2.98 1.36 2.29 2.48 1.79 2.2 2.13 3.43CaO 0.12 0.18 0.24 0.29 0.27 0.33 0.67 5.1Na2O 3.61 5.52 3.95 2.94 3.08 3.22 0.91 0.94K2O 2.31 1.35 2.34 2.49 2.03 2.59 2.3 1.04TiO2 0.7 0.55 1.03 1.14 0.77 1.05 0.7 0.16P2O5 0.05 0.08 0.06 0.06 0.11 0.08 0.04 0.06MnO 0.02 0.01 0.02 0.02 0.03 0.02 0.02 0.05Cr2O3 0.014 0.008 0.017 0.016 0.016 0.018 0.018 <0.002TOT/C 0.05 0.05 0.05 0.08 0.09 0.1 0.03 2.22TOT/S 0.1 0.3 0.05 0.04 0.14 0.11 0.02 <0.02LOI 13.9 11.8 15.6 13.9 9.4 14.2 9.6 9.6

Trace elementsppm ppm ppm ppm ppm ppm ppm ppm

Sc 12 7 15 14 11 16 11 2Ba 170 175 229 261 202 236 216 201Be 4 2 2 3 2 3 1 <1Co 9.7 8.5 12.5 13.5 11.1 13.5 6.9 3.8Cs 4.1 1.9 3.2 4.2 4.2 4.7 3.7 1Ga 19 11.6 22.7 22.7 14.9 23.5 16.9 4.2Hf 7.2 6.4 8.2 8.4 7.5 6.2 6.5 3.7Nb 28.3 19.9 41.3 40.9 20.2 30.4 29.7 4.3Rb 77 42.7 87 83.9 70.4 81.4 78.4 29.3Sn 3 1 4 4 2 4 3 <1Sr 98.9 161 123.2 126.6 94.4 165.9 99.8 88Ta 1.9 1.3 2.6 2.9 1.5 2.1 1.9 0.3Th 11.6 7.7 14.1 15.4 7.8 11.7 9.9 1.9U 8 4 7.1 7.3 6 7.1 5.5 2V 96 56 101 95 78 106 86 21W 1.6 1.1 2.1 1.9 1.1 2.2 1.4 <0.5Zr 272.7 259.3 302 325.5 286 236.1 223.3 138.9Y 18.4 14.7 23.9 28.8 18.9 20 13.8 7.7La 44.2 32 46.5 44.5 27.7 40.1 24.2 8.7Ce 69.3 52.5 75.5 73.4 53.7 62.2 37.7 19.5Pr 8.78 5.76 10.53 9.85 6.37 8.41 5.51 2.21Nd 30 20.8 42.7 38.6 23.5 32.8 21.7 8.4Sm 5.61 3.67 6.92 7.73 4.6 5.89 3.37 1.79Eu 1.04 0.74 1.32 1.51 1.02 1.17 0.67 0.46Gd 4.51 3.19 5.32 6.47 4.02 4.71 2.81 1.51Tb 0.69 0.52 0.87 1.03 0.65 0.74 0.5 0.27Dy 3.46 2.9 4.71 5.26 3.35 4.02 2.56 1.42Ho 0.76 0.6 0.89 1.12 0.7 0.78 0.47 0.31Er 2.16 1.72 2.51 3.18 2.07 2.14 1.45 0.82Tm 0.34 0.25 0.39 0.46 0.31 0.35 0.22 0.12Yb 2.21 1.83 2.6 2.94 2.1 2.17 1.52 0.89Lu 0.33 0.26 0.4 0.45 0.28 0.34 0.24 0.1Mo 6.4 1.3 0.1 <0.1 1.3 0.2 0.2 1.8Cu 10.2 7.8 8.6 8.7 11.9 25.5 10.2 inPb 8.7 5.4 7.8 6 4.3 9.2 5.7 1.6Zn 53 30 52 55 58 63 35 10Ni 26 21 30.9 30 40.4 33.5 16.7 6.3As 4 7.8 1.1 <0.5 6.8 1.7 1.6 2.6Cd <0.1 <0.1 0.09 <0.1 <0.1 <0.1 0.09 <0.1Sb <0.1 <0.1 0.1 <0.1 <0.1 <0.1 0.1 0.2Bi <0.1 <0.1 0.1 <0.1 <0.1 <0.1 0.1 <0.1Hg <0.01 <0.01 0.01 <0.01 <0.01 <0.01 0.01 <0.01Tl 0.1 <0.1 0.1 0.1 0.1 0.1 0.3 <0.1Se <0.5 <0.5 0.09 <0.5 <0.5 <0.5 0.09 <0.5



unique Chado-Libyan paleobiogeographical province. By the end ofthe Miocene, wet environments connected the Lake Chad Basin tothe Libyan Sirt Basin. Families from Sahabi that are shared withToros-Menalla site TM 266 (Chad), the locality that has yielded

Sahelanthropus tchadensis include: Felidae, Hyaenidae, Gomphothe-riidae, Equidae, Suidae, Hippopotamidae, Anthracotheriidae, Giraffi-dae, Bovidae, Muridae, Sciuridae. and Cercopithecidae. Five Generafrom Sahabi that are shared with Toros-Menalla site TM 266 are:Machairodus, Hyaenictitherium, Anancus, Nyanzachoerus, Hexaproto-don, Libycosaurus, Kobus, and ?Hippotragus. Finally, six species thatare shared with Toros-Menalla site TM 266 are: Anancus petrocchii,Nyanzachoerus syrticus, Libycosaurus petrocchii, Kobus darti, and?Hippotragus sp.

Biochronological studies based on comparisons with both Eur-asian and other African Neogene vertebrate faunas suggest an ‘‘in-tra-Messinian’’ age for Member U1 of the Sahabi Formation, ca. 6.8MA and correlative to European Land Mammal unit MN 13 (for areview see Boaz et al., 2008). De Heinzelin and El-Arnauti (1987)related the stratigraphic record of the Sahabi Formation to the‘‘Sahabi Channels’’ first described from seismic data by Barr andWalker (1973). These channels were interpreted as having been in-cised by a large river whose mouth was lowered by the late Mes-sinian desiccation of the Mediterranean. Nicolai (2008) employedseismic and magnetic data to extend the course of the SahabiChannels to the Mediterranean Gulf of Sirt. Remote sensing studiesby Griffin (2002, 2006), Drake et al. (2008, 2009) and Paillou et al.(2009) have lent support to an Eosahabi drainage pattern originat-ing from a Neogene ‘‘Mega-Lake Chad’’ and flowing northward in abroad valley east of the Tibesti Massif. This Eosahabi watershedwould have been separated from the Nile drainage to the east bya low drainage divide corresponding roughly with the modern-day Libyan-Egyptian border.

Consistent with the majority of geological and remote sensingstudies, paleontological results indicate a late Neogene Libyco-Chadian biogeographic province distinct from northeastern andeastern Africa, Afro-Arabia, and the Nile Basin (Boaz et al., 2008;Boaz, 2008). The hypothesis of Carmignani et al. (2009) that theSahabi Channels represent passage of the Nile into the Gulf of Sirtis not supported. Had such a paleohydrographic connection existedone would expect to see the diagnostic presence of anthracotheresin Nile Basin sites such as Wadi Natrun, eastern African sites suchas Fort Ternan and Middle Awash, and Arabian peninsula sites suchas Baynunah. Paleontological data support the interpretation ofPrecambrian sediments making up As Sahabi Formation sedimentsas originating from northern Chad rather than northern Ethiopia.

Fig. 6. SEM images of detrital minerals hosted in the As sahabi sediments (upper:Cr-spinel; lower: zircon).

0.01

0.1

1

10

Cs

Rb Ba Th Pb U K Ta N

b W La Ce P Sr Nd Hf Zr Sm Eu Ti Pr Gd Tb Dy

Ho Er Tm Yb Lu Y Ga

Mo As

Sb

Se

Bi

Sn Co

Zn

Cu Ni V Cr

Sc Cd Be

Hg Tl

Sedi

men

t / U

CC

Fig. 7. Upper Continental Crust (UCC)-normalised (according to Rudnick and Gao, 2003) multi-element diagram (spider diagram) for P25, P28 and P96c As Sahabi sediments,compared to Al Haruj and Wan an Namous—Al Haruj volcanics (Cvetkovic et al., 2010; Bardintzeff et al., 2012).



1

10

100

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Sedi

men

t / C

hond

rite

Fig. 8. Chondrite-normalised REE patterns for P25, P28 and P96c As Sahabi sediments compared to UCC (according to Sun and McDonough, 1989), Al Haruj and Wan anNamous—Al Haruj volcanics (Cvetkovic et al., 2010; Bardintzeff et al., 2012).

0.001

0.01

0.1

1

10

1.0 10.0 100.0

Log

Th/S

c

Log Zr/Sc

MORB

AVERAGEDIABASE

AVERAGEGRANITE

UCCPELAGICCLAYS

AVERAGESHALE

FELSIC

MAFIC

0

5

10

15

0 5 10

La/T

h

Hf

Basic Sources

Mature Sediments

Felsic SourcesSources

Al Haruj volcanics

As Sahabi sediments

Fig. 9. Basic discrimination diagrams (Rollinson, 1993; Totten et al., 2000) for P25, P28 and P96c As Sahabi sediments (open circles: samples from Member U1 of P25 locality;open square: sample from Member U1 of P28 locality; open diamond: sample from Member U1 of P96c locality). Al Haruj and Wan an Namous—Al Haruj volcanics (Cvetkovicet al., 2010; Bardintzeff et al., 2012) are also shown in the Hf-La/Th diagram.



4. Conclusions

Mineralogical and geochemical investigation, performed forfirst time in the literature, of clayey sediments from three locali-ties, P25, P28 and P96c, from fossiliferous Member U1 of the AsSahabi Formation, robustly showed very mature and re-processed

sediments of continental origin, and felsic sources, with no influ-ence from Libyan volcanic (basaltic) rocks. According to our data,the studied As Sahabi sediments can originate in Precambrian con-tinental sources in northeastern Chad. Another scenario could bethat the As Sahabi fossiliferous rocks are related Precambrian out-crops in Ethiopia through an east–west river connection with theNile. We argue this suggestion unfavorable, since it is supportedonly by remote sensing data, and there is no time control and geo-logical data. The abundant vertebrate fauna from the Sahabi For-mation is associated to penecontemporaneous fossil faunas inChad and gives evidence for an Eosahabi River connection to Neo-gene mega-Lake Chad.

Acknowledgments

This research was supported by Shell Exploration and Produc-tion Libya and the Special Account for Research Grants of the Na-tional and Kapodistrian University of Athens. East Libya NeogeneResearch Project is funded by National Science Foundation GrantsBNS-0515591 and BCS 0321893, Shell Exploration and ProductionLibya and the Special Account for Research Grants of the Universityof Athens. The members of ELNRP are thanked for all contributions.The faculty and staff of Earth Sciences Department and the author-ities of Benghazi (formerly Garyounis) University, Benghazi, Libyaare specially thanked for their invaluable support and help in manystages of the present study.

Fig. 10. Complementary discrimination diagrams (Floyd and Leveridge, 1987; Rollinson, 1993; Plank and Langmuir, 1998; Totten et al., 2000; Leybourne and Johannesson2008) for all Member U1 samples from P25, P28 and P96c localities.

Fig. 11. Trace element ratios Ba/Nb vs Zr/Nb for Libyan volcanic rocks and commonmantle reservoirs (Bardintzeff et al., 2012), compared to the sediments of thefossiliferous Member U1 of As Sahabi Formation (present study).



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