GEOLOGIJA 46/1, 113–116, Ljubljana 2003
Chemical composition of Kiscellian silty sediment (sivica) from the Trobni Dol area, Eastern Slovenia
Kemi~na sestava sivice s Trobnega Dola, vzhodna Slovenija
Polona KRALJ & Miha MI[I^ Geological Survey of Slovenia, Dimi~eva 14, 1000 Ljubljana, Slovenia
Key words: Kiscellian silt, sivica, geochemistry, Pannonian basin, Slovenia Klju~ne besede: kiscellijski melj, sivica, geokemija, Panonski bazen, Slovenija
Abstract
Kiscellian marine silt termed »sivica« is widely developed in Tertiary basins of Eastern Slovenia. Chemical composition is rather uniform and reflects the dominance of filosili-cates (mainly illite/muscovite, chlorite and montmorillonite) and carbonates. PAAS normalised REE and Y abundances are slightly depleted for La, Ce, Pr and Nd, very close to PAAS for Sm, Eu, Gd and Tb, and depleted for Y, Ho, Er, Tm, Yb and Lu.
Kratka vsebina
Kiscellijski morski sediment imenovan »sivica« je mo~no razprostranjen v terciarnih bazenih vzhodne Slovenije. Kemi~na sestava je precej enotna in odra‘a prevladujo~ dele‘ filosilikatov (illita/muskovita, klorita in montmorillonita) in karbonatov. Na PAAS normalizirane vsebnosti prvin redkih zemelj ka‘ejo nekoliko ni‘je vrednosti za La, Ce, Pr in Nd, skoraj enake za Sm, Eu, Gd in Tb, in ni‘je za Y, Ho, Er, Tm in Lu.
Introduction
The Trobni Dol area (Fig. 1) forms a part of the La{ko basin – a Tertiary depression, which belongs to the system of Pannonian basins. The La{ko basin is moderately folded and composed of a number of synclines and anticlines (Ani~i} & Juri{a 1985a,b), where pre-Tertiary basement and Tertiary sediments ranging in age from Kiscellian to Pannonian outcrop (Ani~i} et al. 2002).
Sivica is a poorly lithified fine-grained marine sediment which was commonly termed as marly clay or clayey marl in the
past. Sivica is very similar to Kiscellian clay in Hungary according to lithological characteristics and foraminifera fauna (R i -j a v e c 1978, J e l e n et al. 1992). Our studied samples belong to silts, which contain up to 30% of clay and some fine sand. Mineral composition is rather uniform, although the content of minerals is variable. The following minerals were recognised: illite/ muscovite with attached mixed layered clay minerals, chlorite with attached mixed layered clay minerals, kaolinite, Ca-montmo-rillonite, quartz, plagioclase, calcite, dolomite and pyrite. Details of clay mineral
114
Polona Kralj & Miha Mi{i~
Fig. 1. Simplified geological map of the Trobni
Dol area (modified after Buser1977). 1,
Quaternary; 2, Mio-Pliocene clay, silt, sand and
gravel; 3, Oligocene volcaniclastics; 4, Mesozoic
carbonates; 5, triassic keratophyre and tuffs; 6,
Permian and Carboniferous clastic rocks
Sl. 1. Shematska geolo{ka karta obmo~ja
Trobnega Dola (prirejeno po Buserju 1977). 1,
kvartar; 2, mio-pliocenski sedimenti – glina,
melj, pesek in prod; 3, oligocenski
vulkanoklastiti; 4, mezozojski karbonati; 5,
triasni keratofir in njegov tuf; 6, permijski in
karbonski klastiti
composition   are   treated   in   Mi{i~    and Kralj (2002).
This contribution is focused on chemical composition of Kiscellian clastic sediments and its comparison to a widely used post-Archean Australian Shale composite (PA-AS) as they are supposed to represent average crustal relative abundances (Taylor & McLennan 1985). Furthermore, the studies of PAAS (Nance & Taylor 1976) reveal remarkable uniformity of rare earth element distribution. Departures from typical PAAS pattern of rare earth elements, however, can result in tectonically active systems (McLennan et al. 1990), and in diagenesis, weathering and sorting during transport of heavy minerals (Sethi et al. 1998).
Chemical composition of sivica
Two samples from the Trobni Dol area have been analysed (Fig. 1) – from Trobni Dol, near the TDp-1/84 borehole, and from
Brstovnica at Rimske Toplice. Both are surface samples. Chemical composition of the studied sivica samples is rather uniform (Table 1), although minor discrepances in abundance of some major oxides and trace elements were observed. Among major oxides, the content of sodium, manganese and total sulphur is somewhat different. With respect to the high mobility of sodium and manganese, and participation of sulphur in biosphere, the observed differences are not surprising. Bulk chemical composition reflects the dominance of filosilicates and carbonates in the sivica, and relatively low abundance of quartz and plagioclases.
Significant difference in trace element abundance occur only at chromium and nickel, and to some extent at zirconium. Yttrium and rare earth elements (REE) show rather similar content. Some trace elements can be compared to the abundance in PAAS (T a -ylor & McLennan 1985). Rubidium, lead, uranium and REEs are close to the abundance in PAAS, but many other trace elements differ significantly (Table 1). The strontium content is much higher in the sivica samples than in PAAS, and that can be ascribed to the presence of carbonate, which occurs mainly in the form of foraminifera shells. The content of zirconium, hafnium, niobium, barium and thorium is higher in PAAS, and also, the Zr/Hf ratio, but not the U/Th ratio, which is lower than in the sivica samples (Table 2).
Table 1:Chemical composition of two sivica samples
Tabela 1: Kemi~na sestava dveh vzorcev sivice
Oxide/          Unit          Trobni		Brsto
Element       %	Dol	
SiO2	043,57	45,13
TiO2	0,60	0,63
Al2O3	13,92	13,61
Fe2O3	5,42	5,40
Cr2O3	0,014	0,019
FeO	2,8	2,6
MnO	0,17	0,07
MgO	2,70	3,08
CaO	12,99	11,74
Na2O	0,45	0,18
K2O	3,01	2,69
P2O5	0,10	0,13
TOT/C	3,58	3,45
TOT/S	0,37	0,67
L.O.I.	16,9	17,1
Chemical composition of Kiscellian silty sediment (sivica) from the Trobni Dol area,...
115
Element
Unit ppm
Trobni Dol
Brstovnica
Sc
V
Co
Ni
Cu
Zn
Ga
As
Rb
Sr
Y
Zr
Nb
Ag
Cd Sn Sb Cs Ba
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
W
Au
Hg
Tl
Pb
Bi
Th
U
12	12
138	132
19,1	15,3
129	94
26,9	21,6
76	69
22,1	17,7
5,4	7,3
166,3	149,1
348,6	364,5
24,3	25,5
109,1	123,3
11,0	11,5
0,1	<0,1
0,3	0,1
2	2
0,2	0,1
11,5	11,9
269	264
31,6	33,3
60,7	64,4
6,77	7,38
27,5	29,0
5,8	5,7
1,08	1,12
4,65	4,68
0,73	0,79
4,23	4,39
0,80	0,76
2,19	2,32
0,34	0,41
2,33	2,14
0,39	0,38
3,1	3,8
0,9	0,8
1,6	1,4
0,7	0,5
0,09	0,09
0,1	<0,1
19,1	19,7
0,3	0,3
10,8	10,2
2,8	3,6
Rare earth elements (REE) and yttrium, normalised to PAAS (Fig. 2), have shown slight depletion of some light REEs (from La to Nd). Most of the middle REEs – Sm, Eu, Gd and Tb – are close to the PAAS values,
Table 2: Some trace element ratios for the studied sivica samples
Tabela 2: Nekatera razmerja med slednimi prvinami v preiskanih vzorcih sivice
Ratio
Trobni Dol
Brstovnica
Zr/Hf	37,15	36,48
U/Th	0,26	0,26
Nb/Ta	16,16	15,19
Sm/Nd	0,20	0,20
LaN/YbN	1,00	1,15
Eu/Eu*	0,99	1,01
Ce/Ce*	0,98	0,97
and from Dy to Lu, a negative fractionation dominates again. For this reason, the LaN/ YbN ratio, which is commonly used as a measure for fractionation of LREEs against HREEs (Sethi et al 1998) shows no fractio-nation in the sample from Trobni Dol, and only slight fractionation of LREEs over HREEs in the sample from Brstovnica. The depletion of light rare earth elements can be ascribed to the weathering processes. There is practically no europium anomaly in the studied samples, as the Eu/Eu* are close to 1 and to the PAAS value (1,00). Cerium anomalies are also insignificant and slightly exceed that in PAAS which amounts to 0,95. The ratio Sm/Nd, widely used as an indicator of the change in provenance, is constant for both analysed samples.
Fig. 2: PAAS normalised REE + Y patterns for the studied sivica samples
Sl. 2: Na PAAS normalizirane vrednosti prvin
redkih zemelj in yttrija za preiskane vzorce
sivice
116
Polona Kralj & Miha Mi{i~
Conclusions
Chemical composition of both studied sivica samples, from Trobni Dol and Brstov-nica, is rather similar. If compared with PAAS, rubidium, lead, uranium and REEs are close to the abundance in PAAS, but many other trace elements like strontium, zirconium, hafnium, niobium, barium and thorium differ significantly. Strontium is practicaly the only trace element, which is much higher in sivica than in PAAS, and that can be ascribed to the carbonate content. Rare earth elements (REE) and yttrium, normalised to PAAS have shown slight depletion of some light REEs (from La to Nd). Most of the middle REEs – Sm, Eu, Gd and Tb – are close to the PAAS values, and from Dy to Lu, a negative fractionation dominates again. For this reason, the LaN/YbN ratio, which is commonly used as a measure for fractionation of LREEs against HREEs shows no fractionation in the sample from trobni Dol, and only slight fractionation of LREEs over HREEs in the sample from Br-stovnica. The depletion of light rare earth elements with respect to PAAS can be ascribed to the weathering processes. There is practically no europium anomaly in the studied samples, as the Eu/Eu* are close to 1 and to the PAAS value (1,00). Cerium anomalies are also insignificant and slightly exceed that in PAAS which amounts to 0,95. The ratio Sm/Nd indicates that provenance of the sivica sediments probably did not change appreciably. The studies of REEs in Kiscellian andesitic to rhyolitic tuffs of the Kozjansko area (Kralj, 2002) indicate that the contribution of volcanic material in the sivica composition slightly enlarges the abundance of REEs in sivica, so that the normalised values can lie above the PAAS line, but does not influence significantly the shape of REE + Y distribution patterns.
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