TRACE ELEMENT IN DIFFERENT MARINE SEDIMENT FRACTIONS OF THE GULF OF TUNIS: CENTRAL MEDITERRANEAN SEA Noureddine Zaaboub1*, WalidOueslati2, SaadiAbdeljaoued2, F. Javier Huertas3, Alberto LópezLópez--Galindo3Galindo3 1 NationalInstitute of Science and Marine Technology,Technology , SalambooSalamboo,, Tunis,Tunis , Tunisia 2 Science University of TunisiaTunisia,, Manar, Tunis,Tunisia 3 Instituto Andaluz de Ciencias de la Tierra. CSIC ––UGR.UGR. 18002 Granada, Spain *[email protected] Contents Introduction Grain size distribution of surface sediment Mineralogy of different sediment fractions Geochemistry of surface sediment fine fraction Statistical analysis:PCA and Cluster analysis Conclusion Introduction Outlet fo Ghar le Melh Lagoon Outle t o f Mejerda River Mediterranean sea Bizerte N Tabarka Gulf of Tunis Topography of the gulf of Tunis 46 38 N Lagune de Ghar ezla Oued Zerga 39 47 Oued Rh Tunis El Melh 30 31 Ghardimaou 22 40 a n a li a i 23 48 rd Jendouba S je 32 ed d M e ed u u O 41 In the North of Tunisia the major wind period is O 15 24 Kallat Al 33 Oued Tessa Andalous 16 Oued Mellégue 8 25 1 9 17 42 49 marked by strong and frequent North West Sousse 34 Kairouan 2 10 26 18 3 11 35 43 4 19 27 50 direction . Oued Mejerda 5 12 6 13 20 Tunisia 28 36 7 14 Algeria Kaliji Chenal 21 44 51 This wind engenders littoral currents, gyrating 29 37 45 0 5 Km 52 Gammart current anticlockwise forms in the centre of the 0 100 Km gulf, forming weak current in the central part. Sediment dynamics along a littoral zone is Fig1: Study area and sampling sites of closely dependent on the direction and the surface sediment in the north of Tunisia intensity of the littoral currents. The Gulf of Tunis is connected to two principal water flows, the Mejerda River and the Ghar el Melh lagoon. Grain size distribution of surface sediment Silt 0 100 The clayey silt and the sandy silt represent the 20 80 main fractions. 40 60 Clayey silt Sandy silt 60 40 We are interested in the fraction which is <63µm Silty c lay Silty sand that is often selected for geochemical analysis. 80 20 Sandy clay Clayey sand 100 0 Clay 0 20 40 60 80 100 Sand Three surface sediment fine fractions are separated (<2µ, 2-20µ, 20-63µ) for Major and Fig 2: Ternary diagram of particle trace element. size fractions of surface sediment Table 1: particle size fractions of The particles that are less than 2 µm constitute surface sediment less than 63µm the clay fraction, a fine silt fraction (2–20 µm) and a mixture of fine and coarse silt fractions µmµm < 2< 2 22--2020 2020--6363 (20-63 µm). Max 25 80 80 Min 5 30 2 Average 16 60 19 25 Ghar El Melh Ghar El Melh 80 Ghar El Melh 85 24 Lago on Lago on Lago on 80 23 75 75 22 70 21 70 65 37.1 20 37.1 37.1 65 19 60 60 18 a 55 55 a a 17 d r d d r r r r 50 r e 50 j e e 16 e j j e e e v v e e v i 45 i i 15 45 M R R R M 14 M 40 40 13 35 37 37 12 35 37 30 Ca nal 11 Ca nal 30 Canal 25 Khalij 10 Khalij Khalij 25 20 9 8 20 15 10 7 15 6 5 10 5 2-20µ 0 36.9 0- 2µ 36.9 36.9 20-63µ 4 5 -5 10.2 10 .25 10 .3 10.2 10.25 10.3 10 .2 10.25 10.3 Fig3: Distribution of fine fractions of surface sediment in the outlet of Mejerda River In the central zone, the clay and the fine silt fraction are dominant 75-95%. The fine and coarse silt fraction is dominant in the coastal zone. However, in the central zone there is a punctual accumulation by the presence of a region of offshore outcrops. Mineralogy of different sediment fractions Table 2: average of clay minerals and quartz in surfacial sediment Coastal zone smectite Illite Kaolinite Chlorite II--SSquartz < 2 µm 2288 2255 34 55 88 77 22--2020 µm 3300 2244 3344 66 66 1133 2200--6363 µm µm 1188 3333 3322 66 1111 2299 Central zone smectite Illite Kaolinite Chlorite II--SSquartz < 2 µm 2233 2255 4400 55 88 77 22--20 µm 2244 2255 3399 66 66 1155 2200--6363 µm µm 1122 3344 3377 66 1111 3300 Dominant phases are dioctahedral smectite, illite and kaolinite. Chlorite and interstratified illite-smectite are also present. Smectite percentage is higher in the coastal zone compared to the central one. Quartz percentage is almost the same in the coastal zone and the central zone. 0- 2µ 2-20µ 20-63µ 13.5 Ghar El Melh Ghar El Melh 21 Ghar El Melh 34 Lago on 13 Lago on Lago on 20 Smectite and fine Quartz grain 12.5 32 12 19 30 11.5 37.1 37.1 18 37.1 28 11 17 size are accumulated in littoral 10.5 26 a a 10 16 a 24 d d r r d r r r e r e j j 9.5 e e e j 15 e 22 e v e v i e i 9 v i M zone and in the central part of R R M M 14 R 20 8.5 8 13 18 37 7.5 37 37 the Gulf. 12 16 Ca nal Ca nal Ca nal 7 Khalij Khalij 6.5 11 Khalij 14 6 10 12 5.5 9 10 5 Quartz 4.5 Quartz 8 Quartz 8 36.9 4 36.9 7 36.9 6 10.2 10.25 10.3 10.2 10.25 10.3 Ghar El Melh Ghar El Melh 32 29 Ghar El Melh 24 Lago on Lago on 31 28 Lago on 23 27 30 22 The distribution of smectite 26 21 29 25 37.1 37.1 37.1 20 28 24 19 27 23 and fine particles of Quartz 18 22 26 a d 17 21 r 25 r e j 20 e 16 e v 24 i R follow the principal coastal 19 M 15 23 18 14 22 37 37 17 37 13 21 16 drift directions. Ca nal 12 15 20 Khalij 11 14 19 10 13 18 9 12 17 11 8 16 7 Smectite 36.9 Smectite 10 Smectite 36.9 15 9 36.9 6 10.2 10.25 10.3 10.2 10.25 10.3 10 .2 10.25 10.3 Fig 4: Distribution of quartz and smectite in different grain size fration of surfacial sediment Geochemistry of surface sediment fine fraction Total organic carbon shows a low Ghar El Melh Ghar El Melh accumulation in front of Mejerda River Lagoon Lagoon and Ghar El Melah Lagoon. a a d r d er r e Most part of total organic carbon is r e ej j v e i e v R M i R concentrated in the south part of the gulf . M Canal Khalij Canal The C/N ratio shows a terrestrial organic Khalij matter influence mainly in front of Ghar C/N El Melh lagoon (16 ), Mejerda River (12 ) TOC and in the south part of the gulf (17 ). Fig 5: Distribution of TOC and C/N in the surfacial sediment Table 3: Average of major element in surfacial sediment SO3 CaO K2O SiO2 TiO2 MnO MgO P2O5 Na2O (%) Al2O3 Fe2O3 < 2µm 45.91 22.69 8.87 0.02 2.08 0.95 0.29 2.55 1.22 0.17 0.23 2-20µm 51.33 20.32 7.88 0.02 1.85 0.85 0.26 2.26 1.09 0.15 0.25 20-63µm 59.62 17.35 6.39 0.02 1.61 0.75 0.23 1.97 0.95 0.13 0.21 The coarse fraction (20-63µm) in comparison to fine fraction (<2µm) is richer in SiO2 signifying the presence of non-clay minerals such as quartz confirmed by X-ray diffraction. The reverse trend is noticed in Al2O3 and Fe2O3. The weight percentage of MnO remains constant in both fractions with an average of 0.02%. Table 4: Average of trace element in surfacial sediment I V Y Sr Zr Cl Cr Br Ni Pb Zn Ba Ga Co Cu Rb Nb ppm < 2µm 429 223 218 5 72 62 209 31 47 120 196 14 300 28 45 271 25 2-20µm 380 197 192 4 64 55 184 27 42 106 173 12 266 25 40 239 22 20-63µm 333 172 167 4 56 48 160 24 36 93 151 11 230 22 35 208 19 Ghar El Melh The distribution of Pb is homogenous in the three Lagoon fractions . a d r r e j e e v i A little accumulation of Pb is observed in the fine fraction M R Canal (<2µm) in the outlet of Mejerda River (65ppm). Khalij Zn The repartition of Cu, Zn and Zr represent a relative Ghar El Melh accumulation in the fine fraction (<2µm). Lagoon Spacial distribution shows an accumulation of Zn in front a d r r e j e e v i of mejerda river. M R Canal Khalij Pb 1.0 0-2µm Zr Ba MnO Y Statistical analysis 0.5 Na2O MgO Fe2O3 I Pb Zn Cu P2O5 Smectite SiO2 Cl Ni 2 IV K2O t n PCA statistical analysis, identified three e 0.0 Cr m n Al2O3 e p Quartz components that explained 67%, 94% and 64% of m Br TiO2 o I Sr C TOC V II -0.5 Nb the total variance respectively in the three Rb Kaolinite III Ga fractions <2µm, 2-20µm and 20-63µm.