Contr. Mineral. and Petrol. 22, 268--275 (1969)

Diffractometric Clay Mineral Analysis of Recent Sediments of Lake Constance (Central Europe)

GERMAN MULLER and JOOST QUAK]~RNAAT

Received March 6, 1969

Abstract. Mica, smectite, and chlorite are the characteristic clay minerals in about 120 Recent sediment samples of Lake Constance as shown by semiquantitative clay mineral analysis. Interstratified clay minerals are practically absent, kandites were not found.

The decrease of the smectite/mica ratio from West to East is apparently due to the domi- nance of the mica-chlorite assemblage of the Rhine river derived from the northern Alps in the eastern part of the lake. With increasing distance from the delta of the Rhine river, the Tertiary Molass~ clay mineraIs (rnair~y mic~ and smecti~e) derived from r~aks surrounding the lake become more abundant.

Introduction During the last years sedimentological, mineralogical and chemical investigations on Recent sediments of Lake Constance (M~LLE~, 1966a, 1967), as well as of the material brought into the lake by rivers (MOLLER, 1966b ; MOLL]~ and F6RSTN]~, 1968; FOl~STNS~, MOLLSR and REINECK, 1969) were carried ont.

The Rhine river - - draining large parts of the northern Swiss and Austrian Alps - - supplies more than 90 % of the detrital material deposited over %he bottom of the lake, Lake Constance can therefore be considered as a natural settling basin for the Rhine.

The prevailing type of sediments are silty clays and clayey silts. Coarser materials (stirs, silty sands, and sands) are found only in a very narrow strip along the shore in the littoral zone or in deltaic areas. The main constituents of these sediments are quartz, feldspars, carbonates, micas, and clay minerals, the latter being enriched in the fine-grained sediments.

Lake Constance is carved in, and surrounded by, Molasse sediments of Tertiary age (Fig. 1) partly covered by Pleistocene glacial material (ScHmlDL]~, 1911; Sc~Er~c~a, 1968; W A G ~ , 1962).

Volcanic rocks and tufts of Tertiary age are found in the westernmost part of the drainage area (v. E~a~LHAxD~r and W]~ISKI~CHN]~R, 1963). The aim of this study is to present data on the clay mineral distribution in the surface layer of Lake Constance sediments.

Sample Localities; Analytical Procedures

Altogether 120 samples from different traverses were taken with a mud grab permitting to collect undisturbed samples. Only the uppermost 5 cm of the sediment cover were investigated. The sampling localities are shown in Fig. 4.

Diftractometrie Clay Mineral Analysis of Recent Sediments of Lake Constance 269

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Sample preparat ion 1 consisted in separating and disaggregating the clay fraction ( < 2 ~ e . s . d . ) and preparing oriented x-ray slides. Carbonates were dissolved with sodium acetate solution (pH 4.5), 0.01 n NH40tt was used as peptizer.

Magnesium homoiordsed clay has been investigated, Any non-crystalline alumosflicates were not removed. The Phflips commercial s tandard vertical dfffrac- tometer equipped with a transistorised linear recorder with proport ional counter and pulse height discriminator was used. Optimal measuring conditions were chosen for copper radiation for a scanning speed of 1 ~ 2 0/rain. Daily al ignment of the goniometer was achieved with cholesterol (KITTRICK, 1960), To increase efficiency in sample processing, an automat ic changer was used (QvAKV, RNAAT and GASTNE~, 1968). Rout ine traverses were made: a) a run from 2 to 30 ~ 20 of a well assembled, unt rea ted specimen (Mg++. or K+-homoionized), prepared under labora tory atmosphere conditions (20~ C; rel. humidi ty 40 - -60%) ; b) a run from 2 to 15 ~ 2 0 of the glycolated specimen; c) a run from 2 to 15 ~ 2 0 of the 500--550 ~ C calcined specimen (2 hours muffle furnace, air quenched). For supplementary information other 2 0-regions were scanned if this seemed necessary.

To generate a glycol and glycerine atmosphere, a heating box (60 ~ C and 80 ~ C resp.) has been used; specimens rest here for at least 48 hours.

The clay mineral "g roups" , smectite, mica, chlorite, were identified by their characteristic basal x- ray diffraction maxima.

l. Details of sample preparation, x-ray diffraction techniques, mineral-identification proce- dures are described in detail in QVAI~ER~AAT (1968),

270 G. MOLLEIr and J. QUAKERNAAT:

Smectite: Material which expands to a 17 A (001) peak upon glycolation is assigned to smectite; the area under this peak was used as its measure of relative abundance.

Mica clay minerals: The basal sequence 10, 5, 3.3, and 2.5 A which is not affected by glycolation is characteristic for mica-like clay minerals. The 10 A peak area has been taken as a measure of relative abundance.

Chlorite: This mineral group exhibits an integral series of basal reflections with a first basal order reflection of 14 A. The spacings are not affected by glycolation.

Ratios of peak areas from smectite and mica measured within each diffracto- gram were used as a semiquantitative technique.

From the samples of a traverse an average smectite/mica ratio was calculated (Fig. 4). The values vary from the average within narrow limits.

Results

All samples studied had a relatively uniform clay mineral composition. Basal reflections (see Figs. 2 and 3) are well developed on all diffractograms.

From 060 measurements in transmission operation (QtrAK~NAA~, 1968), in comparison with Ward 's standard material, however, it can be assumed that the material as a whole is medium crystallized. In the Untersee (SW par t of Lake Constance), only some samples have been found with poorly organised clay minerals.

Mica-like clay minerals are the main constituents. Some asymmetry of the first basal reflections, the well-known tailing, point to illite-ledikite members. The I001/I002-value varies from 4 to 5, indicating dioetahedral mica derivatives which might be diluted by trioctahedral biotite. Patterns from other reflections are vague, demonstrating broad, relatively intense dioctahedral reflections together with smaller 1.55--1.52 A spacings. Because chlorite is present, it is impossible to state if biotite minerals are present or not. The best descriptive term is probably "of the type Illite > ledikite". For convenience in this paper we define these mica-like clay minerals as "mica".

The relative abundance of mica polytypes cannot be evaluated in most samples, although 1 M d or 1 M polytypes are definitely more abundant in a few samples.

Smectite minerals are generally characteristic of the western part of the lake sediments. After 24 hours ethylene glycol t reatment (in a glycol atmosphere, 60 ~ C) excellent 17 A peaks and clear 17 A shoulders developed (see Fig. 2).

After 48 hours glycerine t rea tment (in a glycerine atmosphere, 80 ~ C) broad 17--18 A peaks and shoulders are visible. When the clay specimen is kept for > 72 hours in a glycerine atmosphere, a definite reflection for the smeetite-glyeerine complex develops (Fig. 3).

Contraction of the lattice was observed for the potassium saturated material; no 17 A reflection was detected for glycolated specimens, only 13--15 ~ plateaus were visible. Thus, glyceration of the magnesium saturated clay is a very slow process and equilibration is clearly a function of time. This reaction is typical for high-charge smectite members. IIigh-charge smectites react like low-charge

I)iffractometric Clay Mineral Analysis of Recent Sediments of Lake Constance 271

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Fig. 2. Typical diffractogram from the western part of the lake. Clay fraction x-rayed at room cendibions (20 ~ C), after ethylene glycol treatment (glycol atmosphere, 60 ~ C) and calcination (520 ~ e)

Fig. 3. :Development of smectite peak after glycerine treatment (glycerine atmosphere, 80 ~ C)

smectite members to liquid glycerine, i.e. they achieve complete equilibrium ; and like vermiculites to glycerine vapor, i.e. only partial equilibrium ( t Ia~w~m) and BU~DL~,u 1966; t~I~DLEu 1966; QVAK~AAT, 1968). The behavior of glycerine for the Mg-homoionised clay - - Mthough a function of inhibition t ime - - is typical for smeetite material.

When pre t rea tment of the substance is insufficient, so tha t the partial equili- br ium state has been achieved, the high-charge smectites will be described as vermiculites (M~)LL~, 1966a).

F rom measurements of b-axis parameters it is very probable tha t the smeetites are dioetahedral.

Chlorite, randomly distr ibuted over the lake area, is a common mineral phase. Both iron enriched as well as magnesium members occur.

Kandite8 were not found. The differential heating 060 reflection test, the inter- salation test with ammonium nitrate, a,s well as the intercalation test with hydra- zinc hydrates (A~D~gw, JacKsoN, and WADA, 1960; QVAK~RNAAT, 1968) were completely negative.

272 G. M/3LLEg etal. : Diffractometric Clay Mineral Analysis of Recent Sediments

Interstrati]ied clay minerals are pract ical ly absent. A few random heteropoly- type clay mineral interstratifieations of the ehlorite/tr iphormic layer type were found in near-Rhine delta samples.

Discussion of Results

The areal distr ibution of the clay mineral assemblage clearly indicates an increase of the smecti te/mica ratio f rom the mouth of the Rhine toward the western par t of the lake (Fig. 4).

Former studies on clay minerals of the suspended load of the Rhine river (MOLL~ and F6~ST~R, 1968) over a period of one year revealed mica -k chlorite as the only clay minerals typical of the alpine source area, mainly consisting of magmat ic and metamorphic rocks. Only during a very short t ime (at the beginning of a highwater period in early summer 1965) a r andom mixed layer smectite-miea- chlorite was observed as additional mineral component .

This alpine mica d- chlorite assemblage is diluted with increasing distance f rom the Rhine delta by a smectite Jr mica -k chlorite (-~ kandite) association derived from the Ter t iary Molasse distributive province s ( L ~ c K ~ , v. ENGELtIARDT, and Ff3C~TBAU~, 1953 ; Ff3CHTBAU~, 1958 ; 1964) and smectite derived f rom Tert iary volcanic tufts (Ho~MANN, 1959; 1961; t tOFMA~ and J X c ~ , 1959; v. E~G~L- ~A~DT and Wv~IsKraCH~, 1963).

The clay minerals derived f rom the Pleistocene sediments covering the Molasse cannot be t raced into the lake deposits since their clay mineral assemblage is identical to tha t of the Rhine river. According to PETERS (1961), Pleistocene glacial sediments are also characterized by a mica + chlorite assemblage. Both Rhine river suspended load and glacial material were derived from the same alpine source area.

The very high smeetite/mica ratio found in parts of the Untersee seems to be strongly influenced by the smeetite derived from surrounding volcanic tufts (Fig. 1).

The very low smectite content of the Gnadensee (northern par t of the Untersee) sediments has been discussed already by SC~6TTL~ (1969): the fine sediments of this pa r t of the lake can be explained as reworked glacial clay deposits, underlying the Recent sediment cover and cropping out in several places of the lake bot tom.

Acknowledgements. The authors are kindly indebted to the Deutsche Forschungsgemein- sehaft for their financial support.

2. Fine-grained sedimentary rocks of the "Older Molasse" (Rupelian, Chattian, and Aquita- nian), which comprise about two thirds of all Molasse rocks, contain illite, montmorillonite, and chlorite while some of their sandstones also carry koalinite (Fi~CHTBAUER, 1964). The problem now arises why no kaolinite was found in any of the Recent Lake Constance sediments studied. Let us assume that half of the Molasse rocks is sandy, the other half being fine-grained and kaolinite-free. Because kaolinite makes up about 20 % of the clay minerals in these sandstones, the total Molasse rocks contain only about 5% kaolinite. Moreover, about 50 % of the fraction analyzed (< 2 ~z) consists of non-clay minerals. Thus, kaolinite would make up only about 2.5 % of the total amount of clay minerals which is clearly beyond the limit of detection. Finally, dilution by the "kaolinite-free" detritus of the Rhine and/or glacial material will further decrease the abundance of any kaolinite present.

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Z u s a m m e n f a s s u n g

A n 120 Sedimentproben aus dem Bodensee wurde der Tonminera lbes tand der F r a k t i o n ~ 2 ~ durch die rSntgenographische Phasenanalyse ha l bqua n t i t a t i v ermit tel t .

Glimmer, Smeeti t und Chlorit shad die charakteris t ischen Tonminera lg ruppen ha den Sedimenten. Mixed-layer-Minerale t re ten so gut wie n icht auf, K a nd i t e k o n n t e n n icht nachgewiesen werden.

Aus der Bes t immung der re la t iven t t~ufigkei t yon Glimmer und Smecti t ergibt sich, da~ das Smect i t /Gl immer-Verh~l tnis yon Osten (E inmi indung des Alpen- rheins) nach Westen stiindig zun immt .

Diese Verteflung ist du tch die Zufuhr yon Glimmer und Chlorit durch den Alpenrhein aus den n6rdl iehen Alpen bedhagt, die jedoch mi t zunehmender En t - fe rnung yore Delta durch die Molasse-Distr ibut iv-Provinz mi t vorherrschend Gl immer u n d Smeet i t i iberlagert wird.

R e f e r e n c e s

BRINDLEY, G. W. : Ethylene glycol and glycerol complexes of smectites and vermiculites. Clay Minerals 6, 237--259 (1966).

ESIGELtI~RDT, W. v., u. W. WEISKIRCtINER: Einfiihrung zu den Exkursionen der Deutschen Mineralogischen Gesellschaft zu den Vulkanschloten der Schw~bisehen Alb und in den Hegau w~ihrend der 39. Jahrestagg. in Tiibingen yore 11.--17. Sept. 1961. Fortsehr. Mineral. 40, 5--28 (1963).

F()RSTNER, V., G. MiFLLER U. H. E. REINECK: Sedimente und Sedimentgeffige des Rhein- deltas im Bodensee. Neues Jahrb. Mineral. Abhandl. 109, 33--62 (1968).

FtiCRTBAUER, H. : Die Schiittungen im Chart und Aquitan der deutschen Alpenvorlands- molasse. Eclogae Geol. Helv. 51 (3), 928--941 (1958).

- - Sedimentpetrographische Untersuchungen in der ~lteren Mol~sse nSrdlich der Alpen. Eclogae Geol. Helv. 57 (1), 157--298 (1964).

HA~WARD, M. E., and G. W. BRINDLEY: Swelling properties of synthetic smectites in relation to lattice substitutions. Clays Clay Minerals 25, 209--222 (1966).

HOFMANN, F. : Vulkanische Tuffhorizonte der Schienerbergeruptionen auf dem Thurgauischen Seeriieken. Eclogae Geol. Helv. 52, 461~475 (1959).

- - Vulkanische Asehen in den Helieitenmergeln des baslerischen, aargauischen und badischen Tafeljuras. Eclogae Geol. Helv. 54, 133--136 (1961).

- - , u. E. J)iG~: Saponit Ms Umwandlungsprodukt im basaltischen Tuff yon Karolihof (Kanton Schaffhausen). Sehweiz. Mineral. Petrog. Mitt. 39, 115--124 (1959).

KrrwRicK, J. A. : Cholesterol as a standard in the X-ray diffraction of clay minerals. Soil Sci. Soc. Am. Proc. 24, 17--21 (1960).

LEMCKE, K., W. v. EI~GELItAI~DT U. H. FUCtITBAUER: Geologische und sedimentpetrogra- phische Untersuchungen im Westteil der ungefalteten~ Molasse des siiddeutschen Alpen- vorl&ndes. Beih. Geol. Jahrb. 11, 1--108 (1953).

MiiLSER, G. : Die Sedimentbildung im Bodensee. 5Iaturwissenschaften 53, 237--247 (1966a). - - The new Rhine delta in Lake Constance. In: Deltas in their geologic framework (edit. by

L. SHIRLEY) Houston Geol. Soc., Houston, 107 p., 1966 (1966b). - - B e z i e h u n g e n zwischen Wasscrk6rper, Bodensediment und Organismen im Bodensee.

Naturwissenschaften 54, 454--466 (1967). - - , u. U. F6~STN~a" Sedimenttransport im Miindungsgebiet des Alpenrheins. Geol. Rund-

schau 58, 229--259 (1968).

Diffractometrie Clay Mineral Analysis of Recent Sediments of Lake Constance 275

PETERS, TJEEK: Tonmineralogische Untersuchungen an Glazialmergeln yon Zollikofen u n d an aqui tanen Torten und Mergeln yon Pieterlen. Schweiz. Mineral. Petrog. Mitt. 41, 71--84 (1961).

QUAKE~NAAT, J. : X-ray analyses of clay minerals in some Recent flnviatile sediments along the coasts of Central Italy. Pubh Fys.-geogr. Lab. Univ. Amsterdam, Nr. 12, 105 p. (1968).

- - , and M. GAST~EI~: A sample changer for oriented clay aggregates in X-ray diffraction. J. Sediment. Petrol. 38, 250--252 (1968).

SCH~IDLE, W. : Zur Kenntnis der Molasse und der Tektonik am nordwestlichen Bodensee. Z. Deut. geol. Ges. 68, 522--551 (1911).

Se~OTTnE, M.: Die Sedimente des Gnadensees - - Ein Beitrag zur Sedimentbildung ira Bodensee. Arch. Hydrobioh, Suppl. 85 (3), 255--308 (1969).

Se~P,I~ER, A. : Untersuchungen zur Ents tehung des Bodensees. Schriften des Vereins fiir Geschichte des Bodensees und seiner Umgebung, H. 86, 283--294 (1968).

WAG~CE~, G.: Zur Geschichte des Bodensees. Jahrb . d. Vereins zum Schutze der Alpen- pflanzen und -Tiere e.V. 27, 1--16 (1962).

Prof, Dr. G. MULLER und Dr. J. QUAKEBNAAT Lab. f. Sedimentforschung 6900 Heidelberg Berliner Str. 19

20 Contr. 5~ineral. and Petrol., u 22