ABSTRACT

Mudrocks and sandstones of Numidian Formation in Sicilyhave been analysed for mineralogical, petrographic, major elementand selected trace element compositions to constrain the intra-formational variability and the sediment provenance. The mudrocksare characterized by a kaolinite-rich signature while the sandstoneshave a quartz-arenitic composition. The high Chemical Index ofAlteration and Plagioclase Index of Alteration strongly suggest thatrecycling processes have been responsible for the present composi-tions. The mudrocks geochemical data suggested a compositionalvariability function of the paleogeographic depositional environments.In particular, the Numidian Formation of the more external SerraDel Bosco Unit is affected by the terrigenous contribution of epicon-tinental-type sediments. With regard to provenance, the geochemicaldata indicate a derivation from post-Archean sedimentary siliciclasticrocks. The contribution of African cratonic sediments was confirmedby the trace elements ratios and by the end-member modellingprocessed on mudrocks compositional data. In particular the suitabilityof the Nubian sediments as one of the sources of sediment supply isalso attested.

KEY WORDS: Numidian Formation, Mineralogy, Geochemi -stry, Provenance, Sicily.

INTRODUCTION

The Oligocene-Miocene Numidian Formation is oneof the most widespread formations in the Mediterraneanregion, outcropping throughout the Apenninic-Maghre-bian Chain, from southern Spain and northern Africa tothe southern Apennines. Owing to its great importance,several studies have been focused on the Numidian For-mation with the majority of them focused on the petro-graphic/geochronologic data of the sandstones (CAZZOLA& CRITELLI, 1987; CRITELLI, 1991; PATACCA et alii, 1992;CRITELLI & LE PERA, 1995; CRITELLI, 1999; CRITELLI etalii, 2011), whilst mineralogical and chemical data ofmudrocks and the chemical analysis of sandstones arestill missing.

In addition some unsettled issues still remain aboutthe compositional variation inside the sedimentationbasin and the role of this Formation in the Neogene paleo -

geoghaphic framework of the Mediterranean area. Themain matter of a long-term debate is the provenance ofNumidian sediment and the location of the source region:this latter has been previously described as northern, fromEuropean terrains (FILDES et alii, 2010, and referencestherein), or southern, from the African craton (THOMAS etalii, 2010, and references therein) supported by geochrono-logical zircon data which indicate Eburnian and Pan-African age, but none Hercynian and Alpine age (seeFILDES et alii, 2010, and reference therein).

The source area must be a region hundreds of thou-sands of km wide, peneplaned for a long time periodand covered by very thick, ultra-mature, quartz-richand kaolinitic regoliths (e.g., GUERRERA et alii, 2012, andreference therein). Around the western Mediterraneanrealm, North Africa is the only regional domain thatsatisfies these requirements whilst no source in Europehas enough surface area to supply the huge amount ofultra-mature and polycyclic siliciclastic detritus requiredfor the Numidian Formation (GUERRERA et alii, 2012).With regard to the supposed source rocks, supporters of asouthern source have variously suggested the ContinentalIntercalaire of western and central Africa (MORETTI etalii, 1991), the Nubian sandstone (WEZEL, 1970; JOHANS-SON et alii, 1998) and Permo-Triassic and Ordovician con-tinental sandstones of southern Tunisia (GAUDETTE etalii, 1979).

In this work, new mineralogical and petro-chemicaldata are discussed in order to: 1) characterize the Numidiansediments also taking into account the effects of sedimen-tary and post-sedimentary processes (MONGELLI, 1993;NESBITT & YOUNG, 1989; NESBITT & YOUNG, 1996;ZHANG et alii, 1998; MONGELLI, 2004; LOPEZ et alii, 2005);2) evaluate the compositional variability inside the forma-tion; 3) evaluate the provenance of sediment by consideringthe major and trace element compositions and consideringthe likeliness of the African provenance hypothesis andthe Nubian Formation as one of the likely sources for theNumidian Formation.

GEOLOGICAL SETTING

The structural framework in Eastern Sicily displays:northward the Calabride crystalline basement, belongingto the European palaeo-margin, overlains the AlpineTethys Units (also known as “Sicilide units”) representingdifferent sectors of an original accretionary wedge formedby broken formations and melange terranes. Southward,the Meso-Cenozoic successions of the subducted Ionian

(*) Dipartimento di Scienze Biologiche Geologiche ed Ambien-tali, Università di Catania, Corso Italia, 57 - 95129, Catania (Italy).Corresponding author: Prof. Paolo Mazzoleni; Address: Corso Italia, 57 -95129 Catania; phone number: +390957195744; fax: +390957195760;e-mail: pmazzol@unict.it

(**) Université de Lausanne, Institut de Géologie et de Paléon-tologie, Lausanne (Switzerland).

(***) National Research Center, Marble and Granite TestingLaboratory Unit, Cairo (Egypt).

Mineralogy and Geochemistry of the Numidian Formation(Central-Northern Sicily): intra-formation variability and provenance evaluation

GIOVANNI BARBERA (*), GERMANA BARONE (*), PAOLO MAZZOLENI (*),DIEGO PUGLISI (*), HASSAN M. KHOZYEM (**) & OSAMA MASHALY (***)

184-R2 – BARBERA

Ital. J. Geosci. (Boll. Soc. Geol. It.), Vol. 132, No. 3 (2013), pp. 00-00, 15 figs., 5 tabs. (doi: 10.3301/IJG.2013.07)© Società Geologica Italiana, Roma 2013

Queste bozze, cor rette deb bo no es serere sti tuite im med i at a mente alla Se g re te riadel la Società Geo log i ca Ital i a nac/o Di par ti men to di Scienze del la Ter raPi az zale Aldo Moro, 5 – 00185 ROMA

Tethys basin are represented by distinct thrust sheetsderived from the deformation of sedimentary successionsreferred to shallow water platforms (Panormide Unit) anddeep-water deposits (i.e., Imerese and Mt. Judica Units).In this framework, the Numidian Formation, represents anew sedimentary supply (GRASSO et alii, 1987) formingthe earliest terrigenous Oligocene-Miocene foredeepdeposit at the onset of collision between the Europeanand African plates: northward the Internal-IntermediateNumidian sequence (GUERRERA et alii, 1992) covers theAlpine Tethydes domain (LENTINI et alii, 1991) whilst tothe south the External Numidian sequence affects thedomains of the Ionian Tethys domain (Imerese basin).

In the study area (fig. 1), the Numidian Formation isformed by three tectonic units: Nicosia, Serra del Boscoand Monte Salici. In all these units the stratigraphicsuccessions consist in mudrocks levels prevailing at thebottom and quartz-arenites prevailing upward; a specificfeature characterizing the upper part of the Serra delBosco Unit is the occurrence of typical glauconitic arena-ceous horizons very similar to the Upper Oligocene-Ser-ravallian levels of the Monte Judica.

The Numidian sedimentation began during Middle-Upper Eocene (JOHANSSON et alii, 1998) in the platform-basin system settled in the Sicilian area at the end of theJurassic to middle Cretaceous ocean rifting stage (CATA-LANO & D’ARGENIO, 1978). From the Early Oligocenethe entire region had been transformed into a shallowopen shelf northward deepening to a trench slope sub-ducting below the Alpine Tethydes accrectionary prismin front of which the foredeep represented the deposi-tional system of the Numidian Formation (BENOMRAN etalii, 1987). The deposition took place on the Panormideplatform and the Imerese basin (MONTANARI, 1987).Northward, also the Alpine Tethydes domain, alreadystructured as tectonic nappes, experienced the deposi-tion of Numidian sediments. Serra del Bosco mudrockswere deposited in a basin intermediate with respect tothe Panormide+Imerese domains and the southeasternAfrican Continental shelf. During Langhian times, aglauconitic sedimentation took place southward in theSicanian-Saccense domain, where the deposition of theepicontinental glauconitic sandstones that form theuppermost part of the Monte Judica Unit occurred;accordingly, the lithological similarities of the Serra delBosco succession with the Monte Judica Unit, drawn bythe occurrence of some glauconitic horizons in the for-mer, could point a likely interference between theirsource and depositional systems.

MATERIALS AND ANALYTICAL METHODS

Thirty-five Numidian mudrocks and nineteen sand-stones were collected for this work. Macroscopically thesandstones mainly consist in massive-hard quartzoserocks whilst the mudrocks are grey to brown (tobacco)and frequently characterized by scaly fabric. For the pur-poses of this work we also analyzed 8 mudrocks sampledfrom the Monte Judica Unit, one kaolin sample and 14sandstones belonging to the Nubian formation (Aswanarea, Egypt; fig. 2).

Regarding the X ray diffraction and X ray fluores-cence, the analytical methodology description are exten-sively reported in recent authors publications (BARBERA

et alii, 2009, 2011). Nine samples were analysed forREE + Cs, Th, U, Hf, Ta, Zn and Sc by iNAA at the SGSmineral service laboratories (Ontario, Canada).

The statistical methodology is mainly based on thelog-ratio technique introduced by Aitchison (1986) andemployed in order to avoid the constant sum problem;the centered logratio transformation (clr) of data is appliedas follows:

x ∈ SD → y = log (xD/gD (x)) ∈ RD

Where x = composition, xD = (x1, x2, ….xD), y = logtransformed composition and gD(x) = D√(x1�x2.........xD).

2 G. BARBERA ET ALII

Fig. 1 - Geological sketch map of the studied area (modified afterCARBONE et alii, 1990).

Fig. 2 - Outcropping area of the Nubian Formation in the northeastern Africa.

This operation transforms the data from their con-strained sample space, the simplex Sd, into the real spaceRd where parametric statistical methods can be appliedto the transformed data. Next the clr-transformed datasetis explored by biplots of two principal components. Bothclr-transformation and biplots processing have beenobtained by means of CoDaPack (THIO-HENESTROSA &MARTIN-FERNANDEZ, 2005).

RESULTS

MUDROCKS: WHOLE ROCK AND CLAY-SIZED FRACTION

MINERALOGY

The whole rock and <2μm mineralogical composi-tions are listed in tab. 1. Quartz is the most abundantcomponent of the non-clay fraction (mean 17 wt.%)ranging from 5 wt.% (sample UN8) to 44 wt.% (UN1).Feldspars can be considered as accessory phases as themean value is 6 wt.% and the range is from 3 wt.% (UMS6-10-11-15) to 14 wt.% (UN1). Very low contents of FeOxides have been detected whilst calcite is almost absentexcept for detectable amounts in samples USB5 andUSB13. Amongst clay minerals kaolinite and smectite arethe most abundant mineral phases (mean 26 wt.%)

characterized by highest values in the order of 50 wt.%(UMS11 and USB12-13 respectively). Illite and chloriteare subordinate phases.

The mineralogy of the <2µm fraction is on the wholecontrolled by kaolinite, and, subordinately by illite andillite/smectite mixed-layered minerals; discrete smectiteand chlorite reach detectable amounts only in few samples(tab. 1). In the diffraction traces, kaolinite minerals arecharacterized by very sharp peaks at 12.3 2θ (0.71 nm)and 24.6 2θ (3.58 nm) and this is suggestive of thick crystals(fig. 3). Mixed-layered minerals exhibit a clear asymmetryin the (001) mica reflection and several weak reflectionsin the 16.29-17.05 2θ region (0.54-0.52 nm) which con-firm the presence of several types of mixed-layeredillite/smectite with different amounts of expandablephases ranging from 20% to 50% with I/S 50 R0 and I/S80 R1 prevailing.

SANDSTONES PETROGRAPHY

The Numidian sandstones composition and textureare well known along all the Betic-Maghrebian Chain andsouthern Apennines. With the aim to compare the Nubiansandstone data we report in tab. 2 the literature composi-tion of the Numidian Sandstones along the Apenninic-Maghrebian Chain. These sandstones are characterizedby a high compositional maturity (more than 95% of

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 3

TABLE 1

Mineralogical compositions of the numi-dian mudrocks.

Whole rock: Qtz=quartz, F=feldspars, Cc=calcite,Fe Ox=Iron Oxides, Tot NC=total non-clayminerals; K=kaolinite, Sm=smectites, Il=illite,Chl=chlorite, Tot CM=total clay minerals. <2µm:I/SR0=illite/smectite mixed layered with 50%of illite, I/SR1=illite/smectite mixed layered with70-80% of illite.

Whole rock <2!m

Sample Qtz F Cc Fe-Ox Tot NC K Sm Il Chl Tot CM DiSm I/SR0 I/SR1 Kao I DiChl UN1 44 14 n.d. n.d. 58 20 n.d. 18 4 42 n.d. 4 32 51 12 1 UN2 11 6 n.d. n.d. 17 36 22 14 10 82 1 35 2 52 10 n.d. UN3 14 7 n.d. n.d. 21 9 32 17 21 79 n.d. 30 26 26 15 2 UN4 10 7 n.d. n.d. 17 22 30 14 17 83 n.d. 39 19 34 7 n.d. UN5 21 5 1 1 28 19 17 25 11 72 n.d. 12 41 36 11 n.d. UN6 18 4 n.d. 1 22 24 21 26 7 78 n.d. 29 31 28 10 1 UN7 7 6 n.d. 1 14 38 20 13 14 86 1 18 10 59 10 2 UN8 5 7 n.d. n.d. 12 42 19 13 12 87 1 19 11 60 10 n.d. UN9 14 6 n.d. n.d. 20 31 25 10 14 79 1 21 5 63 10 n.d.

UN10 12 9 n.d. 1 21 37 20 8 14 79 1 21 12 59 7 n.d. UN11 13 7 n.d. n.d. 19 41 19 13 8 81 1 4 18 68 9 n.d. USB4 29 6 1 2 38 12 17 20 13 62 1 10 42 34 13 n.d. USB5 21 8 3 2 34 20 32 5 9 66 1 40 9 36 13 n.d. USB6 20 7 n.d. n.d. 27 23 23 22 5 73 n.d. 35 20 34 10 n.d. USB7 13 6 1 2 22 18 33 19 8 78 2 50 6 30 12 n.d. USB8 18 6 n.d. 1 25 18 27 25 6 75 1 36 25 26 11 1 USB9 20 5 n.d. n.d. 25 23 27 18 5 74 1 44 6 38 10 n.d.

USB10 27 6 5 3 40 13 30 7 10 60 n.d. 18 76 4 2 n.d. USB11 28 7 1 n.d. 36 14 41 4 5 64 n.d. 35 29 34 2 n.d. USB12 28 6 n.d. n.d. 34 15 41 6 3 66 n.d. 9 48 38 5 n.d. USB13 22 7 3 n.d. 32 11 39 8 11 68 n.d. 9 52 26 10 3 UMS1 12 5 n.d. n.d. 17 26 25 26 6 83 n.d. 39 26 24 8 3 UMS3 7 5 n.d. n.d. 12 9 46 21 12 88 1 40 17 29 11 2 UMS4 12 5 n.d. n.d. 18 28 22 28 4 82 n.d. 17 28 42 12 n.d. UMS5 14 7 n.d. n.d. 21 28 27 18 6 79 1 19 24 47 9 n.d. UMS6 19 3 n.d. n.d. 22 29 28 11 10 77 n.d. n.d. 11 70 19 n.d. UMS7 9 6 n.d. 2 17 37 25 9 11 83 n.d. 28 13 52 5 1 UMS8 23 8 n.d. n.d. 31 27 19 22 2 69 n.d. 23 18 46 13 n.d. UMS9 18 5 n.d. n.d. 24 36 14 23 4 76 n.d. 21 20 50 9 n.d.

UMS10 11 3 n.d. 4 18 22 27 23 11 82 n.d. 18 20 55 7 n.d. UMS11 6 3 n.d. n.d. 9 48 22 17 2 90 1 19 21 48 11 n.d. UMS12 10 7 n.d. n.d. 17 32 25 25 1 83 1 37 8 44 7 2 UMS13 11 6 n.d. n.d. 17 27 31 19 5 83 2 47 n.d. 41 10 n.d. UMS14 15 4 1 1 20 29 27 21 3 80 n.d. 5 32 52 10 n.d. UMS15 28 3 n.d. n.d. 31 28 24 18 n.d. 69 2 55 n.d. 35 6 2

min 5 3 1 1 9 9 14 4 1 42 1 4 2 4 2 1 mean 17 6 2 2 24 26 26 17 8 76 1 26 23 42 10 2 max 44 14 5 4 58 48 46 28 21 90 2 55 76 70 19 3

modal quartz, usually with high/very high roundness) andare commonly ascribed to the quartzarenite clan (sensuFOLK, 1974; fig. 4).

The Nubian Sandstones are often described in litera-ture without detailed microscopic and/or chemical data.Thus, new modal data of these rocks, collected fromsouthern Egypt (Aswan area; Cretaceous Nubian GroupFormations; KHEDR, 1990), are shown in tab. 3 and infig. 4. Detrital frameworks of the Nubian Sandstones arecharacterized by a dominant non-carbonate extrabasinalfraction, made up of abundant sub-angular to sub-rounded quartz grains, very low percentages of feldsparsand lithic fragments (fig. 5). Opaque minerals are oftenpresent as single detrital grains or locally forming abun-dant and very fine-grained interstitial matrix and/orFe-oxide cement. Sili ca cement locally occurs, repre-sented by quartz overgrowths and by other silica-phases,such us chalcedony up to crypto- and or microcrystallinequartz (fig. 5).

4 G. BARBERA ET ALII

Fig. 3 - Air-dried and Ethylene Glycol-solvateddiffraction traces of a representative sample(USB7) showing the mineral phases in the <2µmfraction. I/S = mixed layered illite/smectite, I = illite, K = kaolinite, S = smectite.

Fig. 4 - Total quartz-feldspar-lithic fragment (Qt-F-L) ternary plot ofNumidian sandstones (grey area; see tab. 3 and text for references)and Nubian Sandstones (closed black circles; see tab. 4).

TABLE 2

Composition of the Numidian Flyschsandstones along the Maghrebian-Apen-

nine Chain.

Q=total quartzose grains; F=P+K, where: F=totalfeldspar grains, P and K=plagioclase and k-feld-spar single grains, respectively; L=Lc+Ls+Ch,where: L=unstable fine-grained rock fragments(<0.06 mm) including: Lc=carbonate, Ls=sedi-mentary clasts and Ch=chert; M=micas and/orchlorites in single grains; Om=other mineralgrains (mainly heavy minerals), Mt=siliciclasticmatrix; Cm1=silica cement, Cm2=carbonatecement, Cm3=other cements; n.d.=not determi-ned: 1) CHIOCCHINI et alii, 1980; 2) CRITELLI,1984-1985; 3) MORETTI et alii, 1991; 4) CARBONEet alii, 1987; 5) LOIACONO et alii, 1983; 6) ARDITOet alii, 1985.

Rif Morocco1

Rif Morocco2,

Tell Algeria3

Lucanian Apennine southern Italy4

Lucanian Apennine southern Italy5

Daunian Apennine southern Italy6

n= 8 n= 5 n= 15 n= 15 n= 59 n= 9)

Q 80.7 90.3 83.4 86.8 89.0 70.7 ÷ 81.6 (n. d.) P 0.1 0.2 1.1 1.8 2.7 0.0 ÷ 0.5 K 2.6 0.1 1.7 - 4.2 0.3 ÷ 3.2 Lc - - - 0.0 ÷ 0.9 Lm - - 0.7 (n.d.) - 3.2 (n.d.) 0.0 ÷ 0.8 Ls - - 1.1 - Ch - - 0.3 0.5 - 0.0 ÷ 0.0 M 15.0 - 1.0 0.9 0.1 0.0 ÷0.3 Op - 0.5 1.1 - 0.1 ÷ 0.8 Om - 0.3 0.6 0.3 0.8 0.0 ÷ 0.2 Mt - 1.6 8.6 4.7 - Cm1 - 0.2 - - - 11.7 ÷ 24.1 (n.d.) Cm2 1.6 - 0.6 3.8 - - Cm3 - 6.8 0.9 0.1 - - Sum 100.0 100.0 100.0 100.0 100.0 Q 96.8 99.7 95.6 96.1 89.8 - F 3.2 0.3 3.2 2.1 7.0 - L - - 1.2 1.8 3.2 - Sum 100.0 100.0 100.0 100.0 100.0 -

GEOCHEMISTRY

The chemical compositions of the Numidian mudrocksand sandstones are listed in tabs. 4 and 5 together withthe composition of the Nubian kaolin and sandstones andthe Monte Judica mudrocks. The geochemical data havebeen processed by comparing the elemental abundancesto the global subducting sediment (GLOSS; PLANK &LANGMUIR, 1998).

Mudrocks

The normalised patterns to GLOSS are reported infig. 6 showing a strong depletion in CaO, Na2O and MnOwhereas K2O, SiO2, Fe2O3, MgO and P2O5 are similar tothe GLOSS composition. By contrast TiO2 and Al2O3 arecharacterized by a enrichment with respect to the GLOSS.The trace element patterns normalised to GLOSS are dis-played in fig. 6B, where both XRF and INAA (9 samples)data are reported; amongst the large ionic litophile ele-ments, Sr and Ba are on the whole depleted relative toGLOSS whilst Rb and Cs are slightly to strongly enriched.Thorium and Uranium are slightly enriched.

The transition element are on the whole GLOSS-likeor slightly depleted except Cr, Sc and V that are enrichedreflecting the chief role of clay minerals in their distribu-tions. Finally, HFS elements are characterized by enrichedpatterns with respect to GLOSS.

The behaviour of Monte Judica Miocene mudrocks, alsoshowed in figs. 6A and 6B, is similar to the Numidianmudrocks except for the minor depletions in Na2O and MnOamongst major elements and LILE amongst trace elements.

Concerning the Nubian formation, the kaolin sampleis characterized by several elements below the detectionlimits (tab. 4); nevertheless, the enriched factors for themeasured elements showed significant enrichments inAl2O3 and TiO2 and depletions in CaO and NaO whilst the

SiO2 and P2O5 compositions are similar to the Numidianmudrocks. The trace element pattern is characterized bystrong Ba-Sr and moderate V-Co-Zn depletions and Cr,Th, Zr, Y, Nb, La and Ce enrichments whilst Ni is similarto the GLOSS composition.

The REE Chondrite-normalized patterns (fig. 7) arecommonly observed in the upper continental crust rockscharacterized by LREE enrichment (mean Lan/Ybn = 15.26,tab. 5) and significant Eu negative anomaly (averageEu/Eu* = 0.67, tab. 5).

Sandstones

Sandstones are characterized by an overall depletionin the major elements (fig. 6C). Only silica is enriched inresponse to the quartz-rich signature of the Numidiansandstones. The whole trace elements are depleted withrespect to the GLOSS whilst marked enrichments occuronly for Zr (fig. 6D). The average composition of theNubian Sandstones is also shown in fig. 6 (C, D) the distri-bution of major and trace elements is fairly similar to theNumidian sandstones.

DISCUSSION

SOURCE AREA WEATHERING AND DIAGENESIS

The chemical index of alteration [CIA = 100×Al2O3/(Al2O3 + Na2O + CaO* + K2O)], defined by NESBITT &YOUNG (1982), and the plagioclase index of alteration[PIA = 100×(Al2O3-K2O)/(Al2O3 + CaO* + Na2O-K2O)],defined by FEDO et alii (1996), are both very high forthe overall Numidian mudrocks then suggesting astrongly weathered source. These results are rein-forced by the data plotted into the ACNK ternary dia-gram (fig. 8), where all the studied samples plot near

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 5

TABLE 3

Modal composition of the Nubian Sandstones.

Q=Qm+Qp, where: Q=total quartzose grainsincluding Qm=monocrystalline quartzose grains,subdivided into Qm’=with low undulosity (≤5°)and Qm’’=with high undulosity (>5°), Qp=poly-crystalline quartzose grains which have beensubdivided in Qp’=with few subgrains (≤4crystalline units per grain) and Qp’’=with manysubgrains (>4 crystalline units per grain);F=P+K, where: F=total feldspar grains, P andK=plagioclase and k-feldspar single grains,respectively; L=Lc+Ls, where: L=unstable fine-grained rock fragments (<0.06 mm), including:Ls=sedimentary clasts, Lc=carbonate clastsand Ch=chert; Lt=L+Qp, where: Lt=total lithicfragments (both unstable and quartzose);M=micas and/or chlorites in single grains;Om=other mineral grains (mainly heavy minerals), Mt=siliciclastic matrix; Cm1=Fe-oxidecement, Cm2=Silica cement.

NS 1 NS 2 NS 3 NS 4 NS 5 NS 6 NS 7 1 214 215/216 245 QZ 1 QZ 2 x ! Qm’ 17.5 22.4 18.4 14.6 12.2 15.4 15.4 11.0 32.5 26.2 29.7 11.1 14.3 18.8 7.07 Qm’’ 29.2 28.5 26.5 18.7 17.8 19.2 27.5 19.3 18.2 19.7 14.8 20.3 19.5 21.8 4.70 Qp’ 12.9 15.1 17.1 18.2 19.7 16.3 12.3 19.3 14.7 20.2 26.5 16.3 19.5 16.5 6.11 Qp’’ 25.9 19.7 21.0 26.9 28.3 24.7 23.1 26.1 14.4 1 5.9 6.4 28.1 25.0 22,1 6.42 Ch 3.2 1.3 2.2 2.6 3.6 3.2 1.7 3.1 1.2 2.1 1.2 2.5 2.9 2.5 0.83 Ps - - 0.8 1.4 - 1.2 0.8 - 0.4 - - - - 0.3 0.46 Ks 2.4 2.1 2.1 2.6 2.3 3.5 1.6 3.1 0.8 1.5 1.5 3.8 2.3 2.4 0.84 Lc - 0.7 0.8 0.8 1.2 0.8 0.8 1.2 - - - - - 0.5 0.49 Ls - 2.2 1.9 2.2 2.4 2.7 1.2 3.1 2.4 1.9 1.5 3.3 2.9 2.1 0.87 Ms - - 0.8 0.9 1.8 0.8 - - 0.8 1.1 0.4 - - 0.5 0.58 Op 2.2 1.4 1.9 2.3 1.2 1.6 2.4 1.9 1.6 - 0.8 1.2 2.9 1.6 0.76 Om - - - 0.8 - - 0.4 0.6 - 0.8 - 0.8 - 0.3 0.36 Mt 2.9 2.4 1.9 2.3 3.2 2.2 3.1 1.9 4.4 3.7 4.5 3.1 - 2.8 1.18 Cm1 3.8 4.2 4.6 5.7 4.2 4.5 9.7 6.3 8.6 6.9 12.7 - 4.2 5.9 3.17 Cm2 - - - - 2.1 3.9 - 3.1 - - - 9.5 6.7 1.9 3.09 Sum 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Q 97.4 93.1 92.3 89.2 89.2 86.9 92.8 87.7 94.3 93.7 94.9 88.7 90.6 91.6 3.15 F 2.6 2.3 2.3 4.5 2.6 5.4 2.8 3.6 1.4 1.7 1.8 4.4 2.7 2.9 1.20 L - 4.6 5.4 6.3 8.2 7.7 4.4 8.7 4.3 4.6 3.3 6.9 6.7 5.5 2.34 Sum 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Qm 51.3 55.3 49.4 37.9 34.3 39.8 50.8 35.1 59.9 45.9 54.5 36.8 39.2 46.7 8.66 F 2.6 2.3 2.3 4.5 2.6 5.4 2.8 3.6 1.4 1.7 1.8 4.4 2.7 2.9 1.20 Lt 46.1 42.4 48.3 57.6 63.1 54.8 46.4 61.3 38.7 52.4 43.7 58.8 58.1 50.4 7.2 Sum 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

6 G. BARBERA ET ALII

Fig. 5 - Thin section microphotographs of different Nubian Sandstone samples. Silica cement due (a) to synaxial overgrowths of authigenicquartz on detrital quartz grains and (b) to the formation of chalcedony up to crypto- and microcrystalline quartz; (c) Fe-oxide cement;(d) and (e) feldspar grains; (f) very poor sorting; (g) and (h) same microphotograph with crossed and parallel nicols, respectively, showingfeldspar grains together with polycrystalline and high undulosity detrital quartz grains and Fe-oxide cement.

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 7

Sa

mpl

e

Si

O2

TiO

2 A

l2O

3 Fe

2O3

MnO

M

gO

CaO

N

a2O

K

2O

P2O

5 L

OI

V

Cr

Co

Ni

Rb

Sr

Y

Zr

Nb

Ba

La

Ce

Th

CIA

PI

A

UN

1 NUMIDIAN FORMATION

M

67.4

1.

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2.

30

0.01

1.

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0.16

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2.29

0.

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6.57

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9 97

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84

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6 42

56

6 32

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0.23

1.

89

0.08

13

.3

191

163

14

38

116

175

42

316

47

383

84

166

25

89

96

UN

3 M

54

.2

1.12

19

.8

6.80

0.

03

3.26

0.

61

0.28

3.

22

0.10

10

.6

213

171

24

67

147

184

38

290

35

397

67

122

22

80

92

UN

5 M

54

.0

1.09

20

.1

6.78

0.

02

2.13

1.

34

0.19

2.

57

0.08

11

.8

186

148

20

40

134

179

31

233

32

220

57

118

19

79

87

UN

7 M

49

.8

1.40

25

.1

6.80

0.

04

1.76

0.

68

0.18

1.

93

0.09

12

.3

221

168

19

49

116

172

41

251

48

400

87

155

25

88

95

UN

8 M

50

.2

1.50

26

.2

4.89

0.

01

1.60

0.

61

0.17

1.

97

0.08

12

.8

215

168

11

36

116

182

36

265

49

389

95

179

26

89

95

UN

9 M

56

.4

1.49

23

.6

3.39

0.

02

1.49

0.

16

0.30

1.

94

0.10

11

.1

184

150

14

38

98

147

42

321

39

358

73

142

20

90

97

UN

11

M

53.2

1.

65

26.0

3.

49

0.01

1.

39

0.40

0.

20

2.02

0.

11

11.5

20

0 16

6 10

34

10

9 22

6 45

41

1 49

38

5 10

2 17

8 25

90

97

UN

Q1

S 91

.6

0.28

3.

92

0.55

b.

d.

b.d.

0.

36

0.68

1.

03

0.02

1.

63

5 12

b.

d.

b.d.

14

13

0 5

281

b.d.

20

7 12

18

b.

d.

/ /

UN

Q2

S 95

.8

0.22

1.

81

0.90

0.

01

b.d.

0.

04

0.21

0.

43

0.02

0.

55

b.d.

8

b.d.

b.

d 5

23

6 21

6 b.

d.

90

8 16

b.

d.

/ /

UN

Q3

S 96

.3

0.20

1.

62

0.57

b.

d.

b.d.

0.

05

0.16

0.

27

0.02

0.

80

b.d.

10

b.

d.

b.d

b.d.

20

b.

d.

209

b.d.

70

9

12

b.d.

/

/

UM

S1

M

57.9

1.

22

20.8

4.

02

0.01

1.

77

0.19

0.

16

2.40

0.

05

11.5

17

3 14

7 11

26

12

6 13

3 28

25

3 35

28

1 70

11

4 20

87

97

UM

S3

M

53.0

1.

13

18.6

8.

41

0.04

2.

30

1.60

0.

17

2.29

0.

17

12.3

19

1 17

1 20

40

12

1 19

6 40

25

7 48

19

7 68

12

3 19

78

85

UM

S5

M

56.3

1.

35

22.8

4.

33

0.01

1.

36

0.40

0.

27

2.25

0.

84

10.1

17

6 14

0 15

28

11

4 19

1 48

40

2 37

37

7 83

14

8 20

93

98

UM

S6

M

50.1

1.

50

23.3

7.

62

0.05

1.

50

0.95

0.

39

1.94

0.

19

12.5

20

8 16

7 23

37

11

2 17

3 52

43

4 42

37

1 77

15

5 23

85

92

UM

S8

M

58.3

1.

39

22.0

3.

11

0.01

1.

35

0.30

0.

46

2.68

0.

07

10.4

16

3 13

5 7

18

106

153

32

451

40

401

67

110

22

85

94

UM

S9

M

53.4

1.

52

24.5

3.

46

0.01

1.

24

0.60

0.

21

1.90

0.

16

13.1

16

8 14

7 11

27

10

0 19

4 38

39

9 45

43

4 81

14

4 23

89

95

UM

S10

M

55.4

1.

21

21.7

5.

20

0.01

1.

83

0.64

0.

15

2.27

0.

06

11.5

17

2 15

6 16

27

11

8 18

8 30

29

7 33

31

4 63

12

7 20

85

94

UM

S11

M

51.6

1.

60

27.1

3.

61

0.02

1.

21

0.18

0.

18

2.00

0.

08

12.3

20

8 16

5 16

51

11

8 19

2 51

38

8 53

42

1 10

1 19

5 27

91

98

UM

S13

M

55.0

1.

18

22.3

4.

30

0.02

1.

71

0.88

0.

16

1.93

0.

06

12.4

17

5 13

6 12

27

10

9 19

6 28

27

9 35

34

8 70

13

9 17

85

92

UM

S14

M

54.1

1.

00

21.5

5.

83

0.02

1.

59

2.17

0.

18

2.05

0.

37

11.2

17

9 15

6 14

28

10

8 17

8 29

22

9 26

28

8 57

11

9 27

79

85

UM

S15

M

57.2

1.

44

21.6

4.

55

0.01

1.

59

0.67

0.

32

1.97

0.

08

10.6

16

9 13

4 12

26

11

0 18

6 46

43

9 41

39

8 77

14

9 29

85

93

UM

SQ1

S 95

.9

0.23

1.

97

0.53

b.

d.

b.d.

0.

08

0.29

0.

54

0.02

0.

51

b.d.

9

b.d.

b.

d.

6 28

b.

d.

238

b.d.

22

7 6

27

b.d.

/

/

UM

SQ2

S 91

.5

0.31

4.

34

1.28

b.

d.

0.05

0.

09

0.18

0.

84

0.04

1.

36

10

16

b.d.

b.

d.

15

33

5 21

7 b.

d.

164

12

23

5 /

/

UM

SQ3

S 91

.0

0.28

3.

98

2.05

b.

d.

0.04

0.

09

0.17

0.

77

0.04

1.

57

9 17

5

b.d.

14

32

11

18

6 b.

d.

155

14

21

b.d.

/

/

UM

SQ4

S 96

.4

0.13

1.

61

0.33

0.

01

0.01

0.

09

0.23

0.

39

0.02

0.

85

b.d.

6

b.d.

b.

d.

b.d.

24

b.

d.

106

b.d.

89

6

13

b.d.

/

/

USB

4 M

56

.7

1.13

20

.3

7.09

0.

16

1.78

1.

51

0.23

2.

10

0.11

8.

93

149

121

23

45

99

192

28

266

24

230

46

110

14

80

86

USB

5 M

55

.0

1.07

19

.4

7.62

0.

04

1.26

2.

47

0.12

1.

57

0.12

11

.3

140

120

16

32

73

146

26

311

23

253

43

100

12

76

80

USB

7 M

54

.4

1.23

19

.9

6.52

0.

05

1.74

1.

68

0.47

1.

85

0.05

12

.2

159

133

13

29

97

174

23

238

25

160

50

131

15

78

83

USB

9 M

58

.6

1.33

22

.2

4.41

0.

00

1.06

0.

16

0.11

1.

59

0.07

10

.5

141

126

14

29

89

102

26

257

32

195

58

156

16

92

98

USB

10

M

54.0

1.

05

17.4

6.

75

0.06

1.

44

4.16

0.

30

1.46

0.

10

13.4

13

3 11

3 18

37

81

23

3 27

26

6 24

30

9 35

12

2 10

65

67

USB

11

M

58.7

1.

18

18.5

7.

18

0.06

1.

22

1.30

0.

32

1.30

0.

08

10.2

13

7 11

3 20

34

83

15

7 29

32

2 27

30

8 42

13

8 12

82

86

USB

13

M

54.6

1.

28

19.7

6.

22

0.04

1.

26

2.31

0.

34

2.42

0.

14

11.8

14

4 11

4 13

35

10

3 16

1 32

32

5 28

26

5 46

15

0 14

74

79

USB

Q1

S 93

.7

0.23

2.

94

1.48

b.

d.

0.05

0.

03

0.15

0.

10

0.03

1.

29

5 13

b.

d.

b.d.

b.

d.

19

9 18

1 b.

d.

20

13

21

b.d.

/

/

USB

Q2

S 96

.0

0.21

1.

61

1.04

b.

d.

b.d.

0.

05

0.12

0.

08

0.02

0.

89

5 8

b.d.

b.

d.

b.d.

17

5

244

b.d.

42

11

15

b.

d.

/ /

continue

TABLE4

Chem

ical com

positions ob

tained

by XRF analysis; the UN data have been already published

in B

ARBERAet alii(200

9); M

=Mudrock; S

=San

dston

e; b.d=below

detection

limits.

8 G. BARBERA ET ALII

AG

1

MONTE JUDICA

M

54.0

1.

04

18.1

7.

00

0.12

1.

71

3.11

0.

27

1.50

0.

09

13.0

14

6 12

0 19

44

92

23

2 26

24

2 24

37

6 55

98

14

71

74

AG

3 M

60

.3

1.12

18

.5

7.20

0.

02

1.18

0.

47

0.23

1.

80

0.12

9.

05

142

125

13

34

95

163

26

200

24

228

55

115

13

86

95

AG

4 M

58

.2

1.16

19

.1

7.48

0.

10

1.28

0.

84

0.21

1.

65

0.11

9.

90

149

117

20

38

89

170

28

191

24

280

50

107

14

85

92

AG

5 M

60

.0

1.12

18

.4

7.17

0.

03

1.14

0.

65

0.31

1.

76

0.13

9.

29

140

119

17

35

93

173

29

200

24

441

45

89

13

85

92

AG

6 M

52

.5

1.56

25

.7

5.91

0.

05

1.13

0.

63

0.26

1.

97

0.12

10

.2

176

135

19

36

95

181

33

353

37

569

74

144

17

88

95

AG

9 M

58

.8

1.12

18

.3

5.62

0.

03

1.31

3.

36

0.34

1.

68

0.10

9.

42

115

98

11

32

79

195

27

386

23

402

35

98

11

69

72

AG

10

M

58.5

1.

11

17.8

6.

36

0.04

1.

38

2.76

0.

34

1.75

0.

12

9.79

12

0 10

6 15

36

84

18

5 27

29

4 23

24

1 38

10

3 13

71

75

NS1

NUBIAN FORMATION

S 97

.6

0.51

0.

67

0.58

b.

d.

b.d

0.11

0.

10

0.22

0.

02

0.20

b.

d.

40

b.d.

b.

d.

b.d.

26

10

11

9 b.

d.

52

9 23

b.

d.

/ /

NS2

S

98.0

0.

21

0.62

0.

42

b.d.

b.

d 0.

11

0.17

0.

26

0.02

0.

19

b.d.

7

b.d.

b.

d.

b.d.

22

8

75

b.d.

60

9

6 b.

d.

/ /

NS3

S

98.0

0.

26

0.60

0.

49

b.d.

b.

d 0.

09

0.09

0.

20

0.02

0.

23

b.d.

13

b.

d.

b.d.

b.

d.

25

8 76

b.

d.

56

10

19

b.d.

/

/

NS4

S

97.2

0.

21

0.97

0.

81

b.d.

b.

d 0.

14

0.10

0.

17

0.02

0.

38

7 16

b.

d.

b.d.

b.

d.

24

9 10

4 b.

d.

51

7 26

b.

d.

/ /

NS5

S

97.1

0.

49

0.94

0.

71

b.d.

b.

d 0.

12

0.11

0.

23

0.03

0.

28

4 22

b.

d.

b.d.

b.

d.

30

10

102

b.d.

53

12

20

b.

d.

/ /

NS6

S

97.8

0.

28

0.90

0.

26

b.d.

b.

d 0.

16

0.09

0.

18

0.01

0.

33

b.d.

11

b.

d.

b.d.

b.

d.

21

8 65

b.

d.

65

8 7

b.d.

/

/

NS7

S

78.0

1.

61

7.70

7.

05

0.70

b.

d 0.

63

0.52

0.

94

0.05

2.

79

6 56

25

5

19

96

29

549

14

409

19

61

9 /

/

1 S

96.8

0.

18

0.21

1.

72

b.d.

b.

d 0.

21

0.09

0.

01

0.02

0.

80

23

11

b.d.

b.

d.

b.d.

84

7

87

b.d.

42

8

11

b.d.

/

/

214

S 89

.2

0.78

3.

57

5.06

b.

d.

b.d

0.07

0.

03

b.d

0.02

1.

26

73

25

30

b.d.

b.

d.

17

11

559

13

38

5 11

5

/ /

215/

216

S 88

.5

1.02

6.

89

1.12

b.

d.

b.d

0.05

0.

06

b.d

0.02

2.

32

9 27

10

6

b.d.

20

10

74

3 24

29

13

28

9

/ /

245

S 75

.2

0.98

7.

39

10.1

0.

06

0.87

0.

09

0.22

0.

32

0.08

4.

69

41

39

47

53

10

115

26

372

6 70

31

62

b.

d.

/ /

QZ

1 S

98.4

0.

09

0.07

0.

93

b.d

b.d

0.07

0.

08

0.00

0.

01

0.31

7

7 b.

d.

b.d.

b.

d.

17

6 36

b.

d.

18

5 b.

d.

b.d.

/

/

QZ

2 S

96.7

0.

15

0.12

2.

25

b.d.

b.

d 0.

10

0.08

0.

00

0.09

0.

50

25

5 b.

d.

b.d.

b.

d.

27

8 60

b.

d.

24

9 b.

d.

b.d.

/

/

227

S 94

.4

0.76

1.

51

1.80

0.

02

b.d

0.08

0.

15

0.18

0.

02

1.04

6

22

26

7 b.

d.

26

9 26

0 b.

d.

42

10

13

b.d.

/

/

Kao

M

47

.5

3.38

38

.9

0.87

b.

d.

b.d

0.08

0.

07

b.d.

0.

10

9.84

73

21

3 10

55

b.

d.

53

146

1244

17

9 61

16

7 36

4 34

/

/

continued: T

ABLE4

the A-K line indicating an intense feldspar alteration(NESBITT et alii, 1996). With regard to the sandstones,the major element compositions characterized by verylow Al2O3 contents, make the weathering chemicalindexes above described meaningless. Nevertheless,the high compositional maturity given by the highabundances of detrital quartz grains and by its highand/or very high roundness can be interpreted as testi-fying prolonged transports and, more probably, a poly-cyclic origin of these sandstones. After the deposition,the most significant diagenetic process was the smec-tite-illite transition via the formation of mixed-layeredclay minerals. Mineralogical data and the diffractionpatterns of the analysed samples point up the presenceof not only one kind of interstratification but, in con-trast, different mixed-phases with different propor-tions of illite and smectite layers were recognized; thissuggests that the transition is likely not complete butotherwise it was in progress prior to the involving ofthose terrains in the tectonic events that characterizedthe Formation.

IS THE NUMIDIAN FORMATION HOMOGENEOUS WITHIN ITS

TECTONIC UNITS?

In order to evaluate the compositional variabilitybetween the tectonic units (i.e. Nicosia, Monte Salici,Serra del Bosco) forming the Numidian Formation, themudrocks compositional data have been processed bymeans of multivariate statistical analysis.

The biplots of the first two principal componentscomputed on a subset of selected major (fig. 9A) andtrace elements (fig. 9B) evidenced the relationshipsbetween the four groups; Nicosia and Monte Salici Unitmudrocks are separated from the Monte Judica Unit sam-ples, whereas the cases representing Serra del Bosco Unitshow a very high dispersion with a spread distribution.On the whole, the statistical analysis highlighted that theMiocene succession of Serra del Bosco Unit possesses ageochemical signature that seems to be intermediatebetween the compositions of the other Numidian units(i.e., Nicosia and Monte Salici) and the compositions ofthe Monte Judica mudrocks. This result may be due tothe mixture of strictly Numidian sediments and MonteJudica-like detrital pulses in accordance with the paleo-geographic position of the Serra del Bosco Unit betweenthe Numidian basin and the African continental shelf.

PROVENANCE AND RECYCLING SEDIMENTS ASSESSMENT

The provenance study is mainly based on the mudrocksdata since the quartzarenitic composition of sandstonespreclude many geochemical considerations. A generalevaluation of sediment provenance has been performedby considering the La-Th-Sc relationships (fig. 10A) sug-gesting a derivation from post-Archean sedimentary silici-clastic rocks also confirmed by the (Gd/Yb)ch vs. Eu/Eu*diagram (fig. 10B).

In the Th/Sc vs Zr/Sc diagram (fig. 11), the Numidianmudrocks plot along the zircon addition trend interpretedas due to sedimentary sorting and recycling (MCLENNANet alii, 1993; PERRI et alii, 2013). In this context, the Th/Uratios (ranging from 4.5 to 8.2, tab. 5), on average higherthan values found for GLOSS (4.11) and post-ArcheanAustralian Shale (PAAS) (4.71), may be due to the oxida-

tion and loss of U during erosion and redeposition cycles(MCLENNAN et alii, 1993).

As evidenced by BARBERA et alii (2009) the minera -logical and geochemical features of the Numidian For-mation are in contrast with the compositions of the olderAlpine Tethydes whose provenance from the Europeancrust has been already constrained (BARBERA et alii,2009, 2011); thus the alternative provenance hypothesis(i.e., from the African Craton) has been evaluated. Forthis purpose, several trace element ratios have been con-sidered for the comparison of the Numidian Formationand the Nubian sediments (sandstones and kaolin). Inthe diagram of fig. 12, the mudrocks are well matched bythe Nubian kaolin while the sandstone mimic the Nubiansandstones trends. A further constraining of the Numi -

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 9

UN4 UN6 UN10 USB6 USB8 USB12 UMS4 UMS7 UMS12 SiO2 52.0 56.6 52.5 57.1 55.8 57.0 50.0 52.3 54.9 TiO2 1.30 1.09 1.63 1.34 1.30 1.30 1.28 1.68 1.48 Al2O3 22.6 21.6 25.8 22.0 20.3 20.2 23.0 26.0 23.3 Fe2O3 5.81 4.48 5.03 4.74 7.77 7.93 6.05 5.19 3.60 MnO 0.03 0.01 0.04 0.01 0.01 0.04 0.03 0.01 0.01 MgO 2.68 1.87 1.50 1.27 1.36 1.02 1.71 1.12 1.50 CaO 0.34 0.16 0.17 0.46 0.29 0.52 0.35 0.11 0.10 Na2O 0.19 0.16 0.25 0.19 0.18 0.33 0.16 0.21 0.21 K2O 2.45 2.46 2.01 2.24 2.25 1.84 2.39 1.56 2.03 P2O5 0.08 0.06 0.07 0.06 0.07 0.10 0.08 0.12 0.13 LOI 12.6 11.5 11.0 10.6 10.7 9.70 15.0 11.7 12.7 Sc 20.0 18.2 20.4 17.9 16.9 16.2 19.5 20.4 20.0 V 205 195 195 159 162 153 207 198 185 Cr 180 150 164 141 144 126 174 162 148 Co 18 16 22 12 13 21 20 20 12 Ni 49 40 45 28 22 41 38 41 35 Zn 80 80 100 88 102 101 80 80 70 Rb 136 128 112 110 110 96 135 99 111 Sr 147 134 166 142 146 147 151 188 185 Y 31.0 27.0 48.0 29.2 25.8 33.3 38.0 57.0 38.0 Zr 306 220 416 292 289 266 255 398 353 Nb 36.0 33.0 50.0 25.2 25.5 26.8 34.0 52.0 45.0 Cs 8.3 7.9 6.4 7.4 7.9 5.8 8.3 5.8 7.0 Ba 357 214 456 225 258 356 276 415 320 La 58.2 55.5 74.5 52.9 48.1 54.8 60.2 79.9 63.7 Ce 107 111 142 98 93 109 121 162 119 Nd 42 46 58 43 39 50 55 69 48 Sm 6.9 6.5 10.8 7.2 6.3 8.6 9.2 12.7 8.2 Eu 1.3 1.1 2.2 1.5 1.2 1.7 1.8 2.7 1.6 Tb 1.0 0.8 1.4 0.8 0.6 1.0 1.0 1.4 1.0 Yb 2.8 2.3 3.9 2.6 2.4 3.1 3.0 4.6 3.4 Lu 0.45 0.39 0.61 0.42 0.4 0.47 0.49 0.71 0.54 Hf 8.6 6.6 11.0 7.7 7.3 7.0 7.2 11.0 10.0 Ta 2.2 1.7 2.8 1.5 1.6 1.7 1.5 2.8 2.5 Th 16 13 19 13 14 14 16 20 16 U 2.0 2.6 2.8 2.3 1.7 3.0 2.6 2.8 3.5 (La/Yb)n 19.04 21.98 16.16 11.86 11.92 11.64 16.85 13.55 16.29 Eu/Eu* 0.59 0.56 0.66 0.72 0.69 0.67 0.68 0.73 0.65 Th/U 8 5 6.79 5.65 8.24 4.67 6.15 7.14 4.57 CIA 87 88 90 87 93 91 86 87 86 PIA 96 98 98 97 99 99 95 96 94

TABLE 5

Chemical composition of selected mudrocks obtained by INAA analysis.

dian provenance has been attempted by evaluating theZr/Y vs. Zr/Nb ratios (fig. 13). On the whole, the Zr/Yratio of the studied mudrocks is higher than the relativeaverage values of the magmatic rocks and cratonic shalesreported by CONDIE (1993) and of the Alpine Tethydesreported by BARBERA et alii (2009, 2011). Even if theZr/Y and Zr/Nb ratios may be influenced during the sedi-mentary recycling processes by zircon enrichment(PERRI et alii, 2013), the trend due to the adding of thismineral may not justify the low Y/Nb ratio (0.8-1.2) ofthe Numidian mudrocks. Conversely, the Zr/Y and Zr/Y

ratios of several African alkaline rocks such as theEthiopian and Sudan granitoid suites and the averagecompositions of the cratonic sandstones reported byCONDIE (1993) are characterized by similar or higherratios with respect to the Numidian mudrocks. Worth of

10 G. BARBERA ET ALII

Fig. 6 - Major (A) and trace (B) elements of the analysed mudrocks and sandstones (C, D) normalized to the GLOSS composition (data fromPLANK & LANGMUIR, 1998).

Fig. 7 - REE patterns normalized to chondrite (ANDERS & GREVESSE,1989). Gd* is calculated using the formula: Gd* = (Sm·Tb2)1/3.

Fig. 8 - Molar proportions of Al2O3–(CaO*+Na2O)–K2O plotted intriangular A-CN-K diagram (CaO* represents CaO of the silicatefraction only).

note is that the analysed Nubian kaolin lies in the field ofthe Numidian mudrocks strongly suggesting a likely con-tribution of African sediments. The African provenanceis also accounted by THOMAS et alii (2010) in their exten-sive review about the source of the Numidian Formation,who reported Precambrian zircon ages thus supporting aprovenance from the African Craton.

With the purpose to evaluate the contribution ofthe African Nubian sediments, an end-member model-ling of mudrocks compositional data has been per-formed follo wing WELTJES’s (1997) approach to themixing problem. Starting from initial composition, theend member were iteratively calculated. The analysiswas performed by considering the major oxides,excluding MnO and P2O5 as their contents are veryclose to the detection limits, and excluding K2O inresponse to its high susceptibility to diagenetic trans-formations. The factor variance analysis indicates thatfour end members (high Silica-A, high MgO-B, highAl2O3-C, and high CaO-D) are adequate for the compo-sitional modelling of the selected mudrocks. The com-positions of the initial end members were selected onthe basis of the previous geochemical and paleo-geo-graphical considerations; the end members A, C and Dare representative of the Nubian sandstones, Nubiankaolin and Monte Judica mudrocks respectively. Withregard to the end member B, we decided to considerthe composition of sample UN3 in response to its highMgO contents. The relative contributions of each endmember for each sample are displayed in the histogramsof fig. 14.

The Nicosia and Monte Salici are more influenced bythe African end-members (i.e., A and C) and by the highMgO end-member whereas the Serra del Bosco samples

reflect a higher contribution of the high CaO end memberconfirming the suggested mixing with terrigenous epicon-tinental-type sediments represented by the clays of theMonte Judica Unit. In order to further investigate and toverify the mixing modelling, also the trace elements com-positions were considered; in particular the compositionof end members was calculated by means of ordinaryLeast Squares

The diagram of fig. 15 shows that, even if the absoluteZr values for the high silica (A) and high Alumina (C) endmembers are significantly high, their trace elements pat-terns are as a whole similar to that of the Nubian sand-

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 11

Fig. 9 - Biplots of major (A) and trace (B)elements; the horizontal scale is the firstprincipal components direction (PC1), thevertical scale represent the direction of thesecond principal component (PC2). PC1 + PC2explain the 73% and 66% of the total variancein A and B respectively.

Fig. 10 - A) La-Th-Sc ternary plot; data for reference rocks from CONDIE (1993);B) Eu/Eu* versus (Gd*/Yb)n systematics.

Fig. 11 - Th/Sc vs. Zr/Sc plot (MCLENNAN et alii, 1993; PERRI etalii, 2013).

stones and kaolin respectively, thus supporting the resultsof the major oxides end member modelling.

CONCLUSIONS

A mineralogical and geochemical characterization ofthe Numidian Formation was realized in order to unraveltwo important issues: the compositional variabilityamongst the tectonic units of the Numidian formationand the location of the source area. The statistical analy-sis of compositional data highlighted significant dif -ferences both in major and in trace elements contentsbetween the samples of the Nicosia + Monte Salici Units(Numidian pelites) and Monte Judica Unit (Not-Numidianpelites). By contrast the statistical pattern of Serra delBosco mudrocks seems to be not very clear because of thescattering of the analyzed samples both within the com-

12 G. BARBERA ET ALII

Fig. 13 - Zr/Y vs. Zr/Nb relationships: the following bibliographicdata have been considered: Cratonic shales and sandstones + averageof several magmatic rocks (basalts + andesites + granitoids; CONDIE1993); Alpine Tethydes shales (BARBERA et alii, 2009); Ethiopiangranites (KEBEDE & KOEBERL, 2003; TEKLAY et alii, 1998); Sudangranites and syenites (O’HALLORAN, 1985).

Fig. 12 - Multi-element diagram of selectedratios critical for provenance evaluation. Aparticularly well matching of the kaoliniticmudrocks and the numidian mudrock canbe observed.

Fig. 14 - Histograms of the relative contributions of each end-memberfor each sample: A) high silica end member; B) high magnesium;C) high alumina; D) high calcium.

positional fields of Numidian and not-Numidian mudrocks.The geochemical signature of Serra del Bosco Unit couldbe related to its palaeo-geographic position between theNumidian basin and the continental shelf represented bythe Monte Judica Miocene succession. In this frameworkthe Miocene succession of Serra del Bosco Unit may beconsidered as the result of detrital pulses of sedimentscoming from Numidian source and alternatively fromnot-Numidian source.

The nature of the source rock and the hypothesis ofan African derivation were addressed by considering thetrace elements compositions; the hypotheses that thesource rocks could be located in the African Craton wassupported by the comparative analysis of Numidian For-mation with the Nubian Sandstones and by the results ofend-member mixing modelling that also showed the pos-sible contribution of other sources Hence the results ofour work are consistent with the hypothesis of a southernprovenance of the Numidian debris and indicate that thereworking of older sedimentary sequences was a likelyprocess for the origin of the Numidian debris and thatone of the source rocks could represent by the Nubiansandstones. This conclusion is also supported by thepetro graphic characters of the Numidian sandstones ofall the Apenninic-Maghrebian Chain that are very similarto those observed within Oligocene-Miocene deposits ofthe external Rifian domains (Tangier Unit Auct.; CAZZOLA& CRITELLI, 1987; ZAGHLOUL et alii, 2005), whose prove-nance is exclusively linked to the African Craton.

ACKNOWLEDGEMENTS

We thanks Salvatore Critelli and one anonymus reviewer fortheir constructive comments and suggestions.

REFERENCES

AITCHISON J. (1986) - The statistics analysis of compositional data.Chapman and Hall, London, UK, 416 pp.

ANDERS E. & GREVESSE N. (1989) - Abundances of the elements:Meteoritic and solar. Geochimica et Cosmochimica, Acta, 53,197-214.

ARDITO M.C., COLALUCE G., DAZZARO L., DEL GAUDIO V., LOPS B.,MORESI M., PICCARRETA G. & RAPISARDI L. (1985) - Le arenariedell’Appennino Dauno. Osservazioni geologiche, mineralogiche epetrografiche. Atti 3° Conv. Naz. “Attività estrattiva dei mineralidi II categ.”. ANIM, ed., PEI, Parma, Bari, 50-53.

BARBERA G., CRITELLI S. & MAZZOLENI P. (2011) - Petrology andGeochemistry of Cretaceous Sedimentary Rocks of the Monte Soro

Unit (Sicily, Italy): Constraints on Weathering, Diagenesis, andProvenance. The Journal of Geology, 119, 51-68.

BARBERA G., LO GIUDICE A., MAZZOLENI P. & PAPPALARDO A. (2009) -Combined statistical and petrological analysis of provenance anddiagenetic history of mudrocks: Application to Alpine Tethydesshales (Sicily, Italy). Sedimentary Geology, 213, 27-40.

BASU A. (1985) - Reading provenance from detrital quartz. In: Zuffa G.G.(ed.), Provenance of arenites. Reidel, Dordrecht, 231-247.

BENOMRAN O., NAIRIN A.E.M. & SCHAMEL S. (1987) - Source anddispersal of mid-Cenozoic clastic sediments in the central mediter-ranean region. Mem. Soc. Geol. It., 38, 47-68.

BIANCHI F., CARBONE S., GRASSO M., INVERNIZI G., LENTINI F., LON-GARETTI G., MERLINI S. & MOSTARDINI F. (1987) - SiciliaOrientale: profilo Nebrodi-Iblei. Mem. Soc. Geol. It., 38, 429-458.

CARBONE S., LENTINI F., SONNINO M. & DEROSA R. (1987) - Il FlyschNumidico di Valsinni (Appennino Lucano). Boll. Soc. Geol. It.,106, 331-345.

CATALANO R. & D’ARGENIO B. (1978) - An essay of palinspastic resto-ration across western Sicily. Geologica Romana, 6, 145-159.

CAZZOLA C. & CRITELLI S. (1987) - Litostratigrafia e petrologia dellequarzoareniti torbiditiche oligo-mioceniche di Asilah (Catena delRif, Marocco nord-occidentale). Mineralogica et PetrographicaActa, 30, 203-226.

CHIOCCHINI U., FRANCHI R., GUERRERA F., RYAN W.B.F. & VANNUC-CI S. (1980) - Geologia di alcune successioni torbiditiche cretacico-terziarie appartenenti ai “Flysch Maurétanien” e alla “NappeNumidienne”del Rif settentrionale (Marocco). Studi GeologiciCamerti, 4, 37-66.

CONDIE K.C. (1993) - Chemical composition and evolution of theupper continental crust: Contrasting results from surface samplesand shales. Chemical Geology, 104, 1-37.

CRITELLI S. (1991) - Evoluzione delle mode detritiche delle successioniarenitiche terziarie dell’Appennino meridionale. Mem. Soc. Geol.It., 47, 55-93.

CRITELLI S. (1984-’85) - Provenienza delle torbiditi oligo-miocenichedel dominio esterno e della falda Numidica del Rif (Marocco nord-occidentale). Degree Thesis, University of Calabria, Italy.

CRITELLI S., MUTO F., TRIPODI V. & PERRI F. (2011) - Relationshipsbetween lithospheric flexure, thrust tectonics and stratigraphicsequences in foreland setting: the Southern Apennines forelandbasin system, Italy. In: Tectonics 2 (ed., By Schattner U.),Chapter 6, Intech Open Access Publisher [ISBN 979-953-307-199-1], 121-170.

CRITELLI S. & LE PERA E. (1995) - Tectonic evolution of the SouthernApennines thrust-belt (Italy) as reflected in modal compositions ofCenozoic sandstone. The Journal of Geology, 103, 95-105.

CRITELLI S. (1999) - The interplay of lithospheric flexure and thrustaccomodation in forming stratigraphic sequences in the southernApennines foreland basin system, Italy. Memorie dell’AccademiaNazionale dei Lincei, 10, 257-326.

FEDO C.M., ERIKSSON K.A. & KROGSTAD E.J. (1996) - Geochemistryof shales from the Archean (–3.0 Ga) Buhwa Greenstone Belt,Zimbabwe: Implication for provenance and source-area weathering.Geochimica et Cosmochimica Acta, 60, 1751-1763.

MINERALOGY AND GEOCHEMISTRY OF THE NUMIDIAN FORMATION 13

Fig. 15 - Trace elements compositions of endmembers calculated by means of ordinary LeastSquares (see text for details).

FILDES C., STOW D., RIAHI S., SOUSSI M., PATEL U., MILTON J.A. &MARSHET S. (2010) - European provenance of the Numidian Flyschin northern Tunisia. Terra Nova, 22, 94-102.

FOLK R.L. (1974) - Petrology of Sedimentary Rocks. Austin, Texas,Hemphill Press, 182 pp.

GAUDETTE H.E., HURLE P.M. & LAJMI T. (1979) - Provenance studiesin Tunisia by U-Pb ages of detrital zircons. AAPG Bulletin, 63,456.

GRASSO M., GUERRERA F., LOIACONO F., PUGLISI D., ROMEO M.,BALENZANO F., CARMISCIANO R., DI PIERRO M., GONZALES

DONOSO J.M. & MARTIN ALGARRA A. (1987) - Caratterizzazionesedimentologica, biostratigrafica e mineralogico-petrografica di“successioni miste” inframioceniche affioranti in Spagna (CatenaBetica) e in Italia Meridionale (Monti Nebrodi e Appennino Lucano).Boll. Soc. Geol. It., 98, 175-188.

GUERRERA F., LOIACONO F., PUGLISI D. & ELVIO M. (1992) - TheNumidian nappe in the Magrebian Chain: state of art. Boll. Soc.Geol. It., 111, 217-253.

GUERRERA F., MARTÍN-ALGARRA A. & MARTÍN-MARTÍN M. (2012) -Tectono-sedimentary evolution of the ‘Numidian Formation’ andLateral Facies (southern branch of the western Tethys): constraintsfor central-western Mediterranean geodynamics. Terra Nova, 24,34-41.

JOHANSSON M., BRAAKENBURG N.E., STOW D.A.V. & FAUGÈRES J.C.(1998) - Deep-water massive sands: facies, processes and channelgeometry in the Numidian Flysch, Sicily. Sedimentary Geology,115, 233-265.

KEBEDE T. & KOEBERL C. (2003) - Petrogenesis of A-type granitoidsfrom the Wallagga area, western Ethiopia: constraints from mine-ralogy, bulk-rock chemistry, Nd and Sr isotopic compositions.Precambrian Research, 121, 1-24.

KHEDR E.S. (1990) - Major subdivision of the Red Sea ContinentalMargin Sequence, Southern Egypt. Academy of Scientific Researchand Technology Cairo Bull., 40, 1-15.

LENTINI F., CARBONE S., CATALANO S., GRASSO M. & MONACO C.(1991) - Presentazione della carta geologica della Sicilia centro-orientale. Mem. Soc. Geol. It., 47, 145-156.

LOIACONO F., PAGLIONICO A. & PELLEGRINO M.C. (1983) - Le quarza-reniti del Flysch Numidico di Campomaggiore (PZ): indagini perl’utilizzazione in campo industriale. Geol. Appl. Idrogeol., 18,73-80.

LOPEZ J.M.G., BAULUZ B., FERNANDEZ-NIETO C. & OLIETE A.Y.(2005) - Factors controlling the trace element distribution in fine-grained rocks: the Albian kaolinite-rich deposits of the Oliete basin(NE Spain). Chemical Geology, 214, 1-19.

MCLENNAN S.M. & TAYLOR S.R. (1991) - Sedimentary rocks andcrustal evolution: tectonic setting and secular trends. Journal ofGeology, 99, 1-21.

MCLENNAN S.M., HEMMING D.K. & HANSON G.N. (1993) - Geochimicalaproaches to sedimentation, provenance and tectonics. GeologicalSociety of America Special Papers., 284, 21-40.

MONGELLI G. (1993) - REE and other trace elements in a graniticweathering profile from “Serre”, southern Italy. Chemical Geology,103, 17-25.

MONGELLI G. (2004) - Rare-earth elements in Oligo-Miocenic peliticsediments from Lagonegro Basin, Southern Appennines, Italy:implications for provenance and source area weathering. Int. J.Earth Science (Geol. Rundsch), 93, 612-620.

MONTANARI L. (1987) - Lineamenti stratigrafico-paleogeografici dellaSicilia durante il ciclo alpino. Mem. Soc. Geol. It., 38, 361-406.

MORETTI E., COCCIONI R., GUERRERA F., LAHONDERE C., LOIACONO F.,PUGLISI D. (1991) - The Numidian sequence between Guelma andConstantine (Eastern Tell, Algeria). Terra Nova, 3, 153-165.

NARDI L.V.S., FORMOSO M.L.L., MÜLLER I.F., FONTANA E., JARVIS K.& LAMARÃO C. (2013) - Zircon/rock partition coefficients ofREEs, Y, Th, U, Nb, and Ta in granitic rocks: Uses for provenanceand mineral exploration purposes. Chemical Geology, 335, 1-7.

NESBITT H.W. & YOUNG G.M. (1982) - Early Proterozoic climate andplate motions inferred from major element chemistry of lutites.Nature, 299, 715-717.

NESBITT H.W. & YOUNG G.M. (1989) - Formation and diagenesis ifweathering profiles. The Journal of Geology, 97, 129-147.

NESBITT H.W. & YOUNG G.M. (1996) - Petrogenesis of sediments inthe absebce of chemical weathering: effects of abrasion and sortingon bulk composition and mineralogy. Sedimentology, 43, 341-358.

O’HALLORAN D.A. (1985) - Ras ed Dom migrating ring complex: A-typegranites and syenites from the Bayuda Desert, Sudan. Journal ofAfrican Earth Sciences, 3, 61-65.

PATACCA E., SCANDONE P., BELLATALLA M., PERILLI N. & SANTINI U.(1992) - The Numidian-sand event in the southern Apennines.Mem. Sc. Geol., Univ. Padova, 43, 297-337.

PERRI F., CRITELLI S., MARTÍN-ALGARRA A., MARTÍN-MARTÍN M.,PERRONE V., MONGELLI G. & ZATTIN M. (2013) - Triassic redbedsin the Malaguide Complex (Betic Cordillera-Spain): Petrography,geochemistry and geodynamic implications. Earth-Science Reviews,117, 1-28.

TAYLOR S.R. & MCLENNAN S. (1985) - The continental crust: its com-position and evolution. Blackwell Scientific Publications, Oxford,312 pp.

TEKLAY M., KRONER A., MEZGER K. & OBERHANSLI R. (1998) - Geo-chemistry, Pb-Pb single zircon ages and Nd-Sr isotope compositionof Precambrian rocks from southern and eastern Ethiopia: impli-cations for crustal evolution in East Africa. Journal of AfricanEarth Sciences, 26, 207-227.

THIO-HENESTROSA S. & MARTIN-FERNANDEZ J.A. (2005) - Dealingwith Compositional Data: The Freeware CoDaPack. MathematicalGeology, 37, 773-793.

THOMAS M.F.H., BODIN S., REDFERN J. & IRVING D.H.B. (2010) - Aconstrained African craton source for the Cenozoic NumidianFlysch: Implications for the palaeogeography of the western Medi-terranean basin. Earth-Science Reviews, 101, 1-23.

WELTJE G. (1997) - End-member modeling of compositional data:Numerical-statistical algorithms for solving the explicit mixingproblem. Mathematical Geology, 29 (4), 503-549.

WEZEL C. (1970) - Geologia del Flysch Numidico della Sicilia nord-orientale. Mem. Soc. Geol. It., 9, 225-280.

ZAGHLOUL M.N., DI STASO A., GIGLIUTO L.G., MANISCALCO R. &PUGLISI D. (2005) - First evidence of Lower and Middle Miocenestrata within the succession of the External Tanger Unit: strati-graphy, provenance, palinspastic and geodynamic implications(Intra-Rif Sub-Domain, External Domain; Rif, Morocco). GeologicaCarpathica, 56, 517-530.

ZHANG L., SUN M., WANG S. & YU X. (1998) - The composition ofshales from the Ordos basin, China: effects of sorce weatheringand diagenesis. Sedimentary Geology, 116, 129-141.

14 G. BARBERA ET ALII

Manuscript received 10 February 2013; accepted 28 April 2013; editorial responsability and handling by S. Conticelli.