ANNALES • Ser. hist. na!. • 9 - 1999 • 2 (17) original scientific paper UDC 551.311.2(450.361 Carso) 552.52(450.361 Carso) 87Sr/36Sr i SOTO PIC CHARACTERISATION OF DOLINA SOiLS AND FLYSCH ROCKS FROM TRIESTE AREA (NE ITALY) Davide LENAZ Dipartimento di Scienze deila Terra, 11-3412? Trieste, Via Weiss 8 e-mail: lena2@univ.triest.eJt ABSTRACT ,575//iC5f isotopic analyses have been carried on some dolina soils, sandstones and marl (flyscb) from Trieste area (NE Italy) in order to look for the parent material. By comparison of the obtained results, it is suggested that the main supplies to the genes/5 of these dolina soils are from the rocks constituting the flysch. Ke y words; 8J,Sr/86Sr ratio, Trieste Karst, dolina soils, flysch INTRODUCTION The Sr isotopes can be a powerful tool in studies of chemical weathering and soils genesis, reflecting the sources of Sr available during their formation. Isotopi­caily distinct inputs from soil parent materials allow de­termination of the relative proportions of those materials entering or leaving a natural system. This work gives a first Sr isotopic characterisation of the Trieste Karst soils, and of other sediments outcrop­ping in the area, to evaluate the contribution of the latter in the soil genesis. GEOLOGICA L OUTLINES In the Trieste Karst area (NE Italy), carbonates and different types of sandstones and marls of flysch rocks outcrop (Fig. 1). Cucchi et al. (1987) suggest to call the whole outcropping carbonate sequence as "Trieste Karst Limestone Formation" and to subdivide it in six provi­sional and informal members: Mi. Coste Mbr. (Early Cretaceous p.p.; limestones and lenses of dolostones), Rupingrande Mbr. (Albian p.p.- Cenomanian p.p.; dolostones and calcareous dolostones), Zolla Mbr. (Cenomanian p.p.-Early Turonian p.p.; limestones), Borgo Grotta Gigante Mbr. (Early Turonian p.p,-Senonian p.p.; limestones, lenses of breccia bianco-ro­sea and presence of vadose oolites-pisolites and Mi­crocodium), M.te Grisa Mbr. (Paleocene p.p.; limestones and scattered breccia level), Opicina Mbr. (Paleocene p.p.-Early Eocene p.p.; limestones) (Fig. 2). The "Carbonate Trieste Karst Formation" is sometimes filled by bauxite near the K-T transition (Gregoric et al., 1998), which speaks about moments of sub-aerial exposure. The stratigraphic sequence ended with the interbedded sandstones and marls of the Eocenic flysch. MATERIALS AN D METHODS The soils were sampled in dolinas by means of a hand drill to the depths between 50 and 130 cm. Sr isotopic compositions were measured on whole rock after dissolution of four dolinas soils samples, two unal­tered sandstones and one unaltered marl by an HF­HNO3-HCIO4 mixture in Teflon® vials and standard ion-exchange chromatography using DOWEX A G 50 W X8 resin. Strontium isotopic ratios were measured on a multi-collector Finnigan MA T 262 mass spectrometer at Centra di Studio per il Quatemario e I'Evoluzione Am­bientale (Rome; Italy). Replicate analyses of NBS-987 standard gave an average 87Sr/86Sr ratio of 0.71025 (3), and no corrections were applied for instrumental bias. 87Sr/8f>Sr values, as well as chemical data of the ana­lysed samples (obtained by means of X-ray fluorescence spectrometer; Lenaz eta.1, 1996), are reported in Tab. 1. 239 ANNALES * Ser. hh t nat. 9 1999 2 (17) Davitte U"NAZ: 07$r/*Sr ÎSOTOPIC CM AR ACTE RI S ATtON OF DOllN A SOILS AN D FtYSCH ROCKS FROM TRI ESTE ARE A (NE JTAIY), 239>242 Tab. 1: Chemical analyses (oxides in wt. %, trace ele­ments in ppm) and s~Sr/®6Sr ratio of the studied sam­ples; TR: terra rossa; S: sandstones; M: marl samples. Tab. 1: Kemijske analize (oksidi in utežni odstotki sled­nih mineralov v ppm) in 87Sr^Sr-razmerje anali­ziranih vzorcev; TR: terra rosa; S: peščenjaki; M: pri­merki laporja. TR13 TR19 TR26 TR39 SI S2 MT s;o2 46.76 52.03 50.09 54.78 56.74 44.20 20.20 Ti02 1.08 1.09' 1.23 1.15 0.58 0.32 2.63 : AI2 O3 21.59 19.35 19.41 18.24 8.98 5.74 39.86 ^ Twesre HO 0.71 7.71 1.98 2.05 2.98 2.30 18.05 eocav^cwscM Sag KRHAM CARBOHATV CRETACEOUS CARBONATE d KAft.SViUU» UJU*Î7U> 3AUXJTZ iA-MftE LOClTlDJ' Fe2 03 MnO 10.56 0.18 n.d. 0.18 7.22 0.17 5.56 0.14 n.d. 0.25 n.d. 0.12 n.d. 0.01 MgO 1.59 1.97 1.80 1.86 1.84 1.36 0.14 CaO 1.01 2.22 1.57 1.37 15.78 27.67 0.24 Fig. 1: Geological map of the Trieste area. Full triangle: sandstones; open triangle: marl; open circle: terra rossa; open square: bauxite (Gregorič et al., 1998) Na 2 0 F2 OS 0.42 2.17 0.10 0.71 2.14 0.17 0.48 1.81 0.13 0.83 2.19 0.16 1.35 1.26 0.06 0.70 0.67 0.01 0.08 0.09 0.04 samples. L.O.t. 14.64 12.33 14.66 12.08 10.10 16.87 18.43 SI. 1: Geološka karta tržaške pokrajine. Celotni SUM 100.81 99.90 100.55 100.41 99.92 99.96 99.77 trikotnik: peščenjaki; odprti trikotnik: lapor; odprti krog: terra rosa; odprti četverokotnik: primerki boksita Cr 215 195 204 194 268 133 i 68 (Gregorič et al., 1998). Ni 146 103 118 84 54 48 118 Rb 191 152 146 132 45 27 165 Sr 87 105 106 107 232 404 239 Nb 22 20 20 17 8 5 9 Zr 291 328 306 304 145 120 130 ES «yscx Y 51 51 50 49 31 23 27 Q Qtotomiie Ba 149 526 448 492 149 132 n.d. KKl gg limestone La 21 69 66 58 22 19 n.d. Ce 42 142 161 137 41 37 n.d. ND 21 62 62 55 21 17 n.d. 3 5 !»Sr/SI'Sr 0.75833 0.71762 0.71.594 0,71947 0.7131)1 0.71 S 23 0.72241 m !I) (I I !11 (3) (2! DISCUSSIO N AN D CONCLUSION S irrr-' 87Sr/86Sr isotopic data have been compared to one another, to limestone values taken from literature {Hess ef al., 1986), and to the 87Sr/86Sr value of a KT bauxite outcropping near Padriciano (GregoriC ef al., 1998). These findings reveal that dolina soils have 87Sr/86Sr ra­tios ranging from 0.7159 (1) to 0.71 83 (1), with a mean S value very close to that of the typical terrigenous sedi­mentary materials of the Mediterranean area (about 0.71 7; Dasch, 1969). These data differ not only from the Cretaceous and Tertiary limestone data (0.707 - 0.708; Fig. 2: Stratigraphie column of the Trieste Karst Car- Hess et al., 1986; javoy & Courtillot, 1989), but also bonate Formation (modified from Cucchi et al., 1987). from the B7Sr/86Sr values of the bauxite at the K-T SI. 2: Stratigrafski stolpec karbonatne formacije trža­ transition near Padriciano (0.7080 ± 1; Gregoric et al., škega Krasa (po Cucchi et al., 1987). 240 ANNALES • Ser. hist. nat. • 9 • 1999 • 2 (17) Davide LENAZ; ''Sr^S r ÍSOTOPIC CHARACTOUSATION O f OOUMA SOll.S AKO FLYSCH ROCKS FROM TRIF.STf- AREA tNE (TALY), 239-242 1998). This happens because ali the sediments of the carbonate sequences, and the sediments related to sub-aerial exposure interbedded in, were re-equilibrated in seawater conditions. Samples of flysch show ^Sr/^S r values of 0.7134 (3) - 0.7152 (2) and 0.7220 (2) for sandstones and marl, respectively. The values of terra dolina soils are in­cluded in this range and are intermediate with respect to the ones obtained for sandstone and for marly compo­nents of the flysch itself. in Fig. 3 the flysch and the doiina soils in a K 2 0 vs. s7Sr/86Sr diagram are represented. The samples show a good positive correlation and are best approximate by a second-degree polynomial function (R2=0.97) evidenc­ing that dolina soils could be generated by a mixing of sandstones and marls. In the carbonate K is under 66 ppm (Comin Chiaramonti ef al.r 1982) and the value of 8?Sr/86Sr is lower than 0.708 because this is the value of the pre-Tertiary sea (Hess ef a/., 1986). This fact seems to exclude an important contribution of 87Sr/85Sr from carbonate sequence and bauxite level because it wil l have lowered the isotopic ratio. Moreover, it is possible to notice that TR sample overlying carbonate rocks of different age, TR39 and TR13, have the same 87Sr/86Sr isotopic ratio. O torra rossa 3 ­ A sandstonas (flysch) Afnar l (flysch) O bauxite ( G re goric et al.. 1998) . 2 OCd X. 1 ­ -0 0.706 0.708 0.710 0.712 0.714 In conclusion, the 87Sr/8&Sr data seem to confirm that the flysch components are the best candidate to explain the dolina soils source. In fact previous minera­lógica! studies on the same soils (Lenaz ef a/., 1996) and previous comparisons of the Cr-sptnel crystal-chemistry from dolina soils with the one from the flysch (Carbomn et ai, 1999), indicate the main source of these soils in the flysch material. ACKNOWLEDGEMENTS 1 would like to thank Dr. Angelo De Min and Prof. Riccardo Petrini for their useful suggestions, and to Dr. Francesca Castorina for her isotopic data. 0.716 0.718 0.720 0.722 0,724 s7Sr/86Sf Fig. 3: K20 VS. 87Sr/S6Sr diagram; symbols as in Fig. t. Si. 3: Diagram K20 proti ^Sr^Sr; simboli kot na si. 1. 241 ANNALES • Ser. hist. nat. • 9 • 1999 • 2 (17) Davkto 1.ENAZ-. ^St/^Si ISOTOPiC CHARACTERISATION OF DOtJNA SOILS AMD RYSC H ROCKS f ROM TRIESTE AREA (NE ITALYS, 239.242 87 SR/ 8G S R iZOTOPSK A KARAKTERIZACIJ A PRST I DOLI N I N FLIŠNI H PLAST I I Z OKOLIC E TRST A (S V ITALIJA ) Davide LENAZ Oddelek za zemeljske vede, Univerza v Trstu, 34127 Trieste, Via Weiss 8, Italy e-mail: ienaz@univ.trieste.it POVZETEK Da bi ugotovili izvorne kamnine prsti v nekaterih dolinah v okolici Trsta, srno izvedli87Sr^Sr-izotopske analize teh prsti, flišnih peščenjakov in laporjev. Ob primerjavi dobljenih rezultatov domneva, da gre nastanek prsti v doli­nah pripisati predvsem kamninam, ki sestavljajo tamkajšnji fliš. Ključne besede: razmerje 87Sr/86Sr, tržaški Kras, prst, "doline", fliš REFERENCES Carbonin, S., Menegazzo, G., Lenaz, D. & Princivalle, F. 1999: Crystal chemistry of two detrital Cr - spinels with unusual low values of oxygen positional parameter: Oxidation mechanism and possible clues to their origin. N. Jb. Miner. Mh., H8: 359-371, Stuttgart. Comin Chiaramonti, C., Pirini Radrizzani, C., Stoîfa, D. & Zucchi Stolfa, M. L 1982: Contributo alia conoscenza di alcuni termini carbonatici del Carso Triestino (M.Lanaro - CEDAS). GORTANIA - Atti Museo Friul. Storia Nat., 4:5-30, Udine. Cucchi, F., Pirini Raddrizzani, C. & Pugliese, N. 1987: The carbonate stratigraphie sequence of the Karst of Tri­este (Italy). Mem. Soc. Geol. Ital., 40: 35-44, Roma. Dasch, E. 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