FACIES 46 27-34 I PI. 5 3 Figs. 4 Tabs. ~ Er langen 2002 J

Geochemical and Petrographic Evidence of Meteoric Diagenesis in Tufa Deposits in Northern Dalmatia (Zrmanja and Krupa Rivers, Croatia)

Gordana Pavlovi6, Esad Prohi(,, Slobodan Mike and Darko Tibljag, Zagreb

KEYWORDS: TUFA - SEQUENTIAL EXTRACTION - INSOLUIgLE P, ESII)UE - b, tg, St. Zn, Fc -C()RR}'%ATION - Rt'~CRYSTALLIZATION METEORIC DIAGENESIS - RIVER ZRMAN.IA (CROATIA) RECENT

Summary

Holocene tufa deposits in the Northern Dahnatia re- gion of Croatia occur along the banks and at present sites of waterfalls of the Zrmanja river and its tributary the Krupa river. Petrographic, geochemical and statistical analyses have been used to relate textural features and trace element composition to the degree of meteoric di- agenesis. Trace metal concentrations associated with car- bonate phase were determined by sequential extraction procedure. The insoluble residue (I.R.) is predominantly of primary origin and its amount ranges from 3 c7~: to 29 c~, averaging 13.75 %, thus permitting variable water/rock ratios of the stabilazing meteoric system. All the evidence points to a scarcity of post-depositional recrystallization and cementation, but where present these features are accompanied by I.R., Mg, Sr arid Zn depletion and Fe enrichment.

1 INTRODUCTION

Freshwater carbonates (tufa and travertines) have been investigated extensively last 30 years by means of petro- graphic (hion and Mfiller, 1968; Braithwaitc, 1979: Chafetz and Folk, 1984; Chafetz et al., 1985; Love and Chafetz, 1988; Pedley, 1992; Koban and Schweigert, 1993), geochemical (Cipriani et al., 1972; Jacobsen and Usdowski, 1975; D'Argenio et al., 1981; Herman and Lorata, 1987, 1988; Utech, 1988; Chafetz et al., 1991;) and biological (Winsborough and Golubic, 1987; Pentecost. 1992; Frcytet and Verrecchia, 1998) methods. Calcite precipitation mod- els, especially those dealing with the inlluence of micro- organisms, have recently been the subject of intensive research (Merz, 1992; Yates and Robbins, 1998; Merz- Preiss and Riding, 1999; Castanier et al., 2000).

The Dinaric karst region of Croatia abounds in tufa accumulations presently forming throughout the Plitvice Lakes region and the Krka and Zrmanja rivers areas. The spectacular waterfalls of the Plitvice and ~ k a National Parks have been attracting considerable scientific atten- tion. A series ofhydrochemical (Kempe and Emeis, 1985:

Srdoc e[ al., 1985: Erects et al., 1987) and isotopic (Srdoc et al.. 1985: Srdoc et al, 1994: Horvalincic et al., 2000) studies have been conducted at these sites to determine the process of tufa formation and the age of deposits. The description and inler- preiaiion of naicro-structures of these deposits were ihe pri- mary concerns ol~mly one investigation (Chafctz et al., 1994), while an inlcgrated approach involving both the petrographic and geochemical analyses of tufa deposits are yet to be completed.

No petrographic or geochemical studies have been nlade on tufa accurnulations in the Zrmanja River area despite their widespread occurrence, however, invesligations of the llora have been conducted (Matonickin and Pavletic, 1961, 1962). Consequently, in this paper we establish a model el: meteoric diagenesis of tufa in the Zrman~ia river canyon by describing and interpreting the relationship between petrographic and geochemical features. There is still a paucity of research concerning diagenetic equilibration of low-Mg calcite with meteoric water (Brand and Veizer, 1980: Veizer, 1983). This situation makes our data an ilnportanl addition to the knowl- edge ofcoprecipitation which is an important process that may control the nlobility and fate of dissolved toxic and heavy- metal species in near-surface environments (Reeder el al., 1999).

2 (;ENERAL DESCRIPTION OF THE AREA

"File study area (Fig. I) is situated in the karst region of the southern Dinaridcs in Croatia (Northern Dalmatia). The Cre- taceous limestones are the dominant rock-type exposed at the surface which extend deeply into the subsurface (Ivanovic et al., 1976). Clastic sediments include Paleogenc claslics, Neo- genc clayey marls and Holocene river deposits (Fritz et al., 1978). Morphological cvolulion of the Zrman.ia canyon corm- spends with deformation in the Eocene and Oligocene which produced comprcssional structures striking NW-SE (Fritz, 1972).

Tufa precipitation was mainly during the Atlantic period "'climatic optitnunf' i.e. 5800-3200 yr B.P. and still readily occurs. The region is dominated by a Mediterranean, inostly

Addresses: G. Pavlovid, MSc, Prof. Dr. E. Prohid, l)r. I). Tibljag, Institute of Mineralogy and Petrography, Faculty of Science. University of Zagreb, Horvatovac bb., HR-10000 Zagreb, Croatia, E-mail: gpavlovi@inei.hr: S. Mike. MSc, Institute of Geology. Sachsova 2. HR- 10000 Zagreb, Croatia.

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Fig. 1. Map showing geographical location of the study area (the framed part) as well as expanded view showing the locations of the investigated tufa outcrops (waterfalls: 3-Jankovica buk, I-Berberi buk, and 2-Ogari buk; cascade: 4-Krupa) in the Zrmanja river valley. Nearby town Obrovac marks a downstream direction.

dry climate. Field work is centered around 3 waterfalls at the Zrmanja river and at a small cascade on the Krupa river (Fig. 1). Due to very rugged terrain sampling was random according to accessibility. Samples were taken mostly along the river banks and in some instances from the crest of waterfalls (cascades), where attention was paid to collecting from differing morphologies. Deposits consist mainly of porous tufa associated with luxuriant organic material such as algae and mosses.

3 METHODS

Thin sections were made of representative samples from each group for petrographic description. Prior to slabbing it was necessary to impregnate them under vacuum with epoxy resin because of their crumbly fabric. The micromorpho- logical characteristics were analysed by polarised light mi- croscopy. Phase composition of carbonate matrix and in- soluble residue were determined by the X-ray powder method. The diffraction patterns were taken by means of a d i f f rac tomete r with a propor t ional counter using monochromatised CuK-alpharadiation. Mol % MgCO 3 was calculated on the basis of equations for unit cell parameters as a function of composition (Mackenzie et al., 1983) using the UnitCell program (Holland and Redfern, 1997) results. The organic matter content was determined by loss on ignition. Whole powdered tufa samples were dried at 110~ during 4 hours to drive off any water, and then weighed. Samples were heated to 550~ for a further 2.5 hours and the second weight loss gave the organic matter content. Since elemental analysis of the carbonate fraction of tufa was the aim, a selective dissolution technique was employed (Prohic, 1984). Sample material was disaggregated until the grain size was less than 0.063 mm and then homogenized and ground. A representative 10 g was continually mixing with 325 ml 1M Na-acetate (NaC2H302) for 6 hours. Drops of acetic acid (HC2H302) buffered pH value at 5 were carefully added because lower pH values may result in dissolution of non-carbonate components (Cook, 1992). After dissolution, samples were filtered and weights of insoluble residue were

then subtracted from initial sample amounts to give final sample weights. Digested samples were diluted to 500 ml in a graduated flask and analyzed for cation concentrations using a Pye Unicam Model SP 9 atomic absorption spectro- photometer. Control of the accuracy of AAS was achieved by blind determinations of the geological standard materials GXR2 and GXR5 and it was assessed to be _+5 % (Fe, Mn) or+l 5 % (Zn, Sr). Precision, expressed as variance joined to the laboratory error, was less than 10 %. Magnesium was determined in another laboratory where the accuracy of AAS was controled by 1000-ppm MERCK standard materials, and this together with precision was estimated to be satisfac- tory. Data processing of seven variables was mainly done using the STATISTICt, version 5 program (1995).

4 RESULTS 4.1 Petrology

The collected samples belong to waterfall or cascade morphological type of tufa deposits (Chafetz and Folk, 1984; Pedley, 1990). The most commonly employed group- ing scheme devised to classify samples is one based on the presence or absence of organic constituents incorporated into the deposit (Irion and M/iller, 1968; Love, 1985). Accordingly, the bulk of the samples fit into three types: 1 ) mossy deposits, 2) algally laminated crusts, and 3) algally coated grains.

In hand samples, mossy deposits are highly porous and friable with the I mm diameter holes that record the loca- tions of the basal parts of moss plants when they were alive, and occasional with up to the 2 cm long cavities. Some samples show a trailing habit within the fabric where they originate from sites of water turbulence while, shorter moss fabrics aranged radially are more typical of quiet subaque- ous conditions (M. Pedley, pers. comm., 2001). In thin section, molds of moss stems are concentrically coated by a micrite and microspar cover. This kind of precipitation is explained to be associated with the prokaryote-microphyte biofilms on mosses (Love, 1985; Pedley, 1992). According to Pentecost (1993) the principal texture of this group can be

P l a t e 5 29

P l a t e 5

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Light microscopical photographs of various morphological types of Holocene tufa deposits in the Northern Dalmatia region of Croatia.

Algal veneer on Cretaceous clast devoid of diagenetic features (crossed nichols). Spalite fans. displas, ing sweeping extinction, developed around radiating algal filaments (PhormiUitun % are overlain by algal filaments (SchizothrLv "?) embedded in mJcrite. Krupa cascade. Sample 4/2. Moss tufa characterized by micrite fabric, a generally high porosity (up to 70 %) and lack ofdiagenetic features (plane light). In the left, there is a spar surrounding the algal (Rivularirt ?) I]laments that appears to be a single poikilotopic crystal. Ogari buk wateltilll. Sample 2/4. Moss tufa displaying complex diagenetic forms (plane light). Calcified moss moulds are intensively recrystallized while micritic aggregates restllted fi'om an earlier stage in the evohition of tufa accumulation are typical of peloidal aggregates and fringe cements precipitated by microbial biofihns. Jankovica buk waterfall. Sample 3/7. Algally laminated crust interpreted to be altered by calcite-to-calcite neonaorphism on the basis of geochemi- cal pattern in carbonate phase (plane light). In the centre, there is a continuous spalTy lamina formed by mcrystallization of an initial micritic or sparry calcite phase at the expense of adjacent micrite lamina. This fabric is comparable with that shown on Fig. 3 (Pedley, 1992) and Fig. 18 (Ford and Pedley, 1996) though. Jankovica buk waterfall. Sample 3/6/1.

described as microcrystalline aggregates composed of pe- loidal, clotted or structureless micrite with unoriented xenomorphic crystals.

In hand specimens, algally laminated crests range from porous, friable deposits to dense, cemented deposits with alternating laminations up to 4 mm thick. In thin section. seasonally controled alternating bands of micrite and sparite

(Irion and Mtiller, 1968) are precipitates due to both inor- ganic and organic processes within mucilage sheath (Love, 1985) which sunounds the 0.005 mm dialneter cyanophyte filaments. In one sainple (3/6/1) aggradational neomor- phism was identified (PI. 514) which resulted in large colum- nar crystals grown at the expense of the surrounding micrilic layers (Love and Ctlafetz, 1988). However, this polycyclic

30

Fig. 2. Log-transformed values of the insoluble residue (I.R.), organic matter (Org.) and trace elements (Mg, Fe, Mn, Sr and Zn) present in tufa smnples from the Zrmanja and Krupa rivers are given in a downstream direction represented by an arrow. On horizontal axis, the first numbers designate localities while the second (and the third) numbers represent ordinal numbers of the samples.

isopachous fringe cement sequence is interpreted (Pedley, 1992; Ford and Pedley, 1996) to be the result of temporary procaryote-microphyte fihn colonization (peloidal micrite) and inorganic precipitation (pallisade spat'). Both of these explanations (altered vs unaltered fabric) can be taken into consideration here but, the overall geochemical evidence points to a substantial diagenetic modification of primary tufa fabric.

Algally coated grains up to 15 cm diameter are formed by clasts of Cretaceous limestone with the cortices developed as a by-product of microbial colonization of their surfaces. Their thickness is similar to the laminations seen in the algal crusts. A soft, bumpy surface of the upper portion of clast and hard, smooth surface of the bottom of clast are typical. In thin section, they are composed of two ahernating layers (Love, 1985): i) V-shaped clumps of filamentous cyanobac- terial "bushes" encased in several elongate spar crystals, and 2) individual subparallel cyanobacterial filaments incrusted by micrite (PI.5/1).

In addition to scarce occun'ences of recrystallization, minor amounts of cement are present in large cavities due to enhanced permeability. Isopachous cements, lining cavity walls, are composed of equant rhombohedral or bladed crystals up to 0.1 mm in length and up to 0.05 mm in width. Equant, random mosaic cements occur as pore-filling ce- ments increasing in size (up to 0.03 mm) towards pore centers. Meniscus cements consist o1' anhedral and/or rhom- bohedral crystals ranging in size from 0.01 mm to approxi- mately 0.05 ram.

4.2 Mineralogy

The predominant mineral in the deposits is low-Mg calcite where mole % MgCO 3 does not exceed 3 %. Quartz, 10,~ phyllosilicate (illite and/or mica), chlorite, plagioclase, K-feldspar and smectite (expandable clay) were detected in the insoluble residue, while in one sample from the Krupa river dolomite was also detected. The diffi'action patterns did not show any signs of calcite. This proves that an applied segment of the selective dissolution technique (Prohic, 1984) is an effective leaching procedure for calcite whereas not so effective for dolomite.

4.3 Geochemistry

A total of 20 samples were analysed for the insoluble residue and organic matter contents and trace element con- centrations (Tab. 1). The general trend of these results according to downstream direction represented by the right- hand side of the Figure 2 is also presented. Chemical data from the intensively altered samples (3/3/1: thin black lamina as an imprint of post-depositional reductive microen- vironment and 3/6/1: aggradational neomorphism) and the sample of distinct origin and morphology (4/2: algally coated grain) were not included in biwtriate and multiwtriate analyses. These statistics are sensitive to outlying observa- tions and can be inflated by only a few atypical values (Prohic et al., 1997).

31

Sample IR ()rg. 1"r Mn Sr Mg Zn

1/2 22 2 140 237 153 3948 33 2/t 16 1 124 130 154 1415 .g,0 2/2 17 3 131 127 150 1312 41 2/3 15 2 112 209 135 145(~ 29 214 29 3 132 236 181 32116 I~,

215 16 I t35 130 141) 1472 28 2/6 18 2 139 185 175 163"; 30 2/8 14 3 150 127 156 1445 34 3/1 11 3 236 713 12~) 1121 31 3/2 17 3 228 285 135 1561 30 3i312 13 3 217 184 I16 I V~8 2X 314 14 2 220 127 145 1561 31 3/5 15 2 199 148 120 1226 ~{ 31612 10 4 203 140 1 I I 1044 27 317 I0 3 178 167 114 l~_~v' -.'>', 411 7 3 ")'~ . . . . _~6 161 108 I ~,~'9 )'~ 4/4 6 2 144 166 138 2183 32 Other 31311 16 4 3(J3 1217 124 1365 30 3/6/1 3 2 242 122 ,~8 1(!3(I 24 4/2 6 9 138 65 217 2383 36

Table 1. Results of geochemical analyses. 'Other' represents results excluded from the bivariate and multivariate statistics. All trace elements are given in ppm, I.R. and Org. in %.

4.3.1 Univariate and bivariate statistics

The basic statistical parameters for 7 variables in 20 tufa samples are shown in Table 2. Prior to bivariate and multi- variate analyses the trace element data was subjected to log transformation because trace elements are frequently log- normally distributed due to geological processes (Rose et al., 1979). Correlation coefficients for the investigated variables are given in Table 3.

4.3.2 Multivariate statistics

Since a minimum of 100 samples and 20 variables are necessary for factor analysis, factors calculated (Ward's method, 1-Pearson) in this study are not stable and their joint behavior towards variables can be considered to be only approximate (Tab. 4). It is important to note that neither

factor controls most of the variance for the I.R., Fe and Mn, what would otherwise represent leaching of these two ele- ments during acid digestion of the samples from the I.R.

Structure (Fig. 3) organised by Q-cluster analysis (Ward's method, I-Pearson) shows that all 17 tufa samples arc chemically homogenous, because the samples morphologi- cally distinctive and/or from the different localities show similar chemical composition. On the contrary, morphologi- cally similar and/or from the same localities show different chemical composition.

5 DISCUSSION

A survey of the results (Tab. 1) demonstrates the gener- ally high insoluble residue (I.R.) content and low concentra- tions of cations (Sr, Mg, Zn, Fe, Mn) indicative of precipi- tation in a freshwater environment. Much of the insoluble

11.1t6

C3

II.lJ4

_C J

rL I lJ.O[J

Samples tI,41 (241

Fig. 3. Vertical icicle plot (Q-cluster analysis). Numbers along horizonlal axis represent the numbers of samples (e.g. the first number of sample 3/3/2 corresponds to sampling locality 3 i.e. Jankovica buk. while the second and the third number designate that the second half of the third sample in a row from this site was analyzed). All variables are log-transformed.

residue come from the source area of the Zrmanja river and is represented by Anizian age strata composed of schists, sandstones, calcareous marls and dolomites ([vanovic c1 al., 1976). D'Argenio et al. (1981) postulated that diagenetic modifications in tufas depend on the permeability, which can vary greatly in lufa deposits. The insoluble residue reduces the original permeability, retarding dissolution of the original carbonate phase and the diffusion and flow transport rates between water film and the surrounding meteoric bulk aquifer water (Brand and Vcizer, 1980). Cipriani et al. (I 972) proposed the possibility to determine

w'hether the insoluble residue was essentially a postgenetic or syngcnetic feature based on its correlation with Sr. in the laUcr case, calcite should preserve original Sr conccntration so that correlation with I.P,. would be strongly positive. This relationship (Tab. 3) was observed also by Pa\,lovic (2001). The mode of incorporation of Sr in calcite has been ex- plained in recent papers (Paquettc and Reedcr, 1995; Reeder

et al., 1999). Tufa samples display the wel l -known fact about

coprccipitation of Sr. Mg and Zn in calcite by their mutual positive correlations, and also by their positivc correlations with I.R. (Tab. 3). Positive correlations of organic matter with Fe and Mn (Tab. 3) arc consistent with anaerobic microbial processes involved in oxidalion o forganic matter. Efficiency of migration c,i Fe 2+ into a diagenetic carbonate

phase is much lcss in the presence of high I.R. resulting m their negative correlation (Tab.

n Mean I X.icdmn IR 20 13 75 Ii "; Or~ 20 2 85 "; Fc 2(t l 7(7 85 I~4

Mn 20 243 8 1(,35 M~ 24) 1667 2 I15u 5 Sr 20 13995 136 5

-'Zn 20 , 31 1 :m

,I Mm ',..la'x I v, tddc~ 2~; [ 5 0,3~7

i ~/ I 6031) ti2 3()'~ 52 3764 65 1217 264 546

I )'~0 3048 743 4' "~'~._ '~8 217 28 W06 24 41 4 r

Tab. 2. Basic statistics o[-alI trace elements in ppm, I.R. and Org. in c/~.

32

I.R ()r~. Fe Mn Sr Mg Zn I.R. t.00 ()r~, -0.16 I 0 0 Fe -0.44 042 100

Mn 0 0 7 0 2 2 0.30 I 00 Sr I).70 -0 35 -0.64 -001 100 M~ 043 -0.16 -0 41 O. 1 I 0.58 1.00 Zn 0 4 6 -0.15 -0.50 -0.09 0.69 0.32 I 0 0

Tab. 3. Tufa samples correlation coefficients (bold type numbers are significant at p < 0.05; n = 17). All variables are log- transformed).

The above discussion is in accordance with results of our factor analysis (Tab. 4). Factor 1, which controls most of the variance for I.R., Fe, Sr, Mg and Zn, represents diagenetic equilibration in an aerobic microenvironment whereas, the second factor shows anaerobic microenvironmental con- trols on diagenesis (Tab. 4). Nevertheless, the insoluble residue and the organic matter represent independent vari- ables. Controls on carbonate geochemistry, especially those concerning the amount and the mineralogical composition of the insoluble residues, have been clearly established (Fltigel, 1968; Fltigel, 1982).

The model explained above will be tested on texture- chemistry covariance in order to compare the diagenesis of one sample to another whereby determining which sample is less altered, and therefore has the more original trace ele- ment concentrations. This interpretation will be discussed separately for each of the three samples that have been marked out as the examples of low textural maturity (2/4) with respect to high textural maturity (3/6/1 and 3/7).

Sample 2/4, which belongs to moss tufa, was taken at the river bank above the level of the present-day water table 30 m downstream from the Ogari buk waterfall. In hand speci- men, the friable and clayey fabric abounds in < 1 mm diameter closely packed holes, while large cavities are completely lacking. In thin section (PI. 5/2), high porosity (up to 70 %), fragile lace-like texture, empty molds of algal and moss origin, and micritic framestone are predominantly exhibited. No evidence of post-depositional neomorphism or cementation was observed. This tufa is supposed to have originated in the area permanently submerged where the abundances of mosses and algae are intermixed in propor- tions favoring the latter. Its low degree of diagenesis is best demonstrated (Fig. 2) by the increased concentrations of Mg, Sr and Zn, the highest I.R. content and one of the lowest Fe concentrations.

log I.R. Io~ ()r~. I% Fc Io1~ Mn 1o~ Sr log Mg Io~ Zn Ei~envalue % or Var

Factor ] Factor 2 * 081 002

0 24 * 0 6 6 * - 0 6 3 * 058

0 lg * 0 84 * 0.91 -021 * 0 73 0 06 * 0 7 2 -0 20

3 26 131 4(158 ] 8 76

Tab. 4. Varimax rotated factor analysis of Holocene tufa samples (n = 17) from the Zrmanja and Krupa rivers.

Sample 3/6/1, belonging to algally laminated crusts, was taken at the river bank 10 m upstream from the Jankovica buk waterfall. This I cm thick veneer, formed on the moss tufa, composed of alternating light and dark undulatory laminae, was the hardest and the most dense sample in a whole series. The only microscopic feature (PI. 5/4) is the calcite-to-calcite neomorphic sequence, proposed by Love and Chafetz (1988), as a consequence of enlargment of elongate sparry crystals that encrust cyanobacterial fila- ments. This kind of recrystallization was attributed to am- monia from decomposing algae (Love and Chafctz, 1988). Described diagenetic alteration is supported by the lowest I.R. content, significant decreases in Mg, Zn and Sr concen- trations, and one of increased Fe concentrations.

Sample 3/7, which belongs to moss tufa, was taken from the fall splash zone at the Jankovica buk waterfall. Since aquatic mosses flourish and occupy a substantial part of this zone, their morphologies are recognizable in the fabric of the sample as trailing well cemented coatings. The most notice- able diagenetic alterations are recrystallization of moss incrustations (P1.5/3) and cementation; the latter feature is better developed in this specimen than in any of the previous examples. This textural maturity is accompanied by chemi- cal trends (Fig. 2) of decreased I.R., Mg, Sr and Zn values, and increased Fe value.

Since the trace element concentrations in tufa depend on the trace elemental composition of the precipitating waters, it is important to stress that contrary to the Zrmanja river, the drainage area of the Krupa river is almost completely repre- sented by carbonate rocks. Therefore, the comparison of texture-chemistry covariance between tufa from these two rivers is not appropriate. Considering the Zrmanja river data alone (Fig. 2) it is possible to discern a partial similarity of the I.R., Mg, Sr and Zn curves, and also a partial mirror image of Fe curve.

6 CONCLUSION

Tufa deposits from the Zrmanja and Krupa rivers were studied in order to present the first petrologic and geochemi- cal research on Holocene Croatian waterfall tufas, including descriptions of morphology and texture, chemical composi- tion and diagenesis. The investigated tufa samples have been classified into three types: (1) mossy deposits, (2) algally laminated crusts, and (3) algally coated grains. Carbonate phase is composed of low-Mg calcite with no more than 3 mole % MgCOy The insoluble residue (I.R.), averaging 13.75 %, is constituted of quartz, 10 ,~. phyllosilicate, chlo- rite, plagioclase, K-feldspar and smectite. Strong positive correlation (r -- 0.7) between Sr and I.R. is an indication that the latter is mostly of the primary origin, and not the result of karstic processes. Elemental concentrations are low ac- cording to a freshwater environment of precipitation, aver- aging 1667 (Mg), 140 (Sr), 31 (Zn), 180 (Fe) and 244 (Mn) ppm. The generally low intensity of diagenesis is mainly due to the fact that these tufas are quite young (Holocene age), and also due to a high insoluble residue (I.R.) content which inhibits the activity ofdiagenetic meteoric water. Diagenetic

33

equil ibrat ion of l o w - M g calci te is exempl i f i ed by the tex-

ture-trace e lement model . Increasing textural alteration,

including recrystal l izat ion and cementa t ion , is accompanied

by the decrease of I .R. , Sr, Mg and Zn and the increase of Fe.

A c k n o w l e d g e m e n t s

Field and laboratory research was funded by the Ministry

of Sc ience and Techno logy of Croat ia through the Project

No. 119305. Research was conducted for fulf i lment of the

first au thor ' s Mas te r ' s degree. The first author is thankfull to

Jozica Zupanic for an immense help during the study. We

thank to Marta Cov ic for measur ing the trace e lement

concentra t ions by A A S technique. We are sincerely grateful

for the rev iews by H. M. Pedley (London) and editors E.

Fltigel and E. Fl t igel-Kahler (Erlangen); the paper has greatly

benefi t ted f rom their valuable commen t s and suggest ions.

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Manuscript received July 28, 2001 Revised manuscript received October 10, 2001