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Use of immobile trace elements for the correlation of Telychian bentonites on Saaremaa Island, Estonia, and mapping of volcanic ash clouds/Immobifsete mikroelementide kasutamine Telychi bentoniitide korrelatsiooniks Saaremaal ja vulkaaniliste tuhapilvede kaardistamine.
Abstract:
Thirty suspected altered volcanic ash (bentonite) samples from the Nassumaa-825 and Orissaare-859 sections were analysed by the X-ray fluorescence method. Twenty of these samples revealed chemical signs of pure volcanogenic material, one was of mixed terrigenous-volcanogenic origin, and nine were classified as terrigenous claystones. Twenty of the bentonites were correlated, with variable confidence, with bentonites from earlier studied sections; one sample represents a formerly unknown eruption. New and earlier published bentonite correlations were used for tracing the diachronous nature of the Rumba-Velise formations boundary and for composing new isopach schemes of six Telychian bentonites. Key words: bentonites, K--bentonites, Telychian, correlation, isopach schemes, East Baltic.

Rontgenfluorestsentsmeetodil on analuusitud kolmekummet oletatavat vulkaanilise tuba (bentoniidi) proovi Nassumaa-825 ja Orissaare-859 puursudamikest. Selle tulemusel on selgunud, et 20 neist on pubtad vulkanogeensed setted, uks vulkanogeense ja terrigeense materjah segu ning ubeksa terrigeensed savid. Bentoniitidest 20 korreleeruvad varem teada olnud vulkaaniliste kihtidega; uks uuritud bentoniitidest (Orissaare 91,5 m) esindab uut, varem mitte teada olnud vulkaanipurset. Uusi ja varem avaldatud korrelatsioone on kasutatud Rumba ja Velise kihistu piiri diakroonsuse jalgimiseks ning bentoniitide leviku ja paksuse skeemide koostamiseks.

Article Type:
Report
Subject:
Bentonite (Analysis)
Bentonite (Chemical properties)
Bentonite (Natural history)
Terrigenous sediments (Analysis)
X-ray spectroscopy (Research)
Stratigraphic correlation (Analysis)
Authors:
Kiipli, Tarmo
Orlova, Kiira
Kiipli, Enli
Kallaste, Toivo
Pub Date:
03/01/2008
Publication:
Name: Estonian Journal of Earth Sciences Publisher: Estonian Academy Publishers Audience: Academic Format: Magazine/Journal Subject: Earth sciences; Science and technology Copyright: COPYRIGHT 2008 Estonian Academy Publishers ISSN: 1736-4728
Issue:
Date: March, 2008 Source Volume: 57 Source Issue: 1
Topic:
Event Code: 310 Science & research
Product:
Product Code: 1452000 Bentonite NAICS Code: 212325 Clay and Ceramic and Refractory Minerals Mining SIC Code: 1459 Clay and related minerals, not elsewhere classified
Geographic:
Geographic Scope: Estonia Geographic Code: 4EXES Estonia
Accession Number:
199194719
Full Text:
INTRODUCTION

Altered volcanic ash beds (bentonites, K-bentonites, metabentonites, tonsteins, feldspathites) in sedimentary sections provide an important proxy for ancient volcanic activity on a scale of hundreds, and sometimes thousands of kilometres (Fisher & Schmincke 1984). Volcanic ashes, deposited almost instantly in a geological sense, may serve as perfect, chronologically fixed marker horizons for stratigraphy (Thorslund 1945; Batchelor & Jeppsson 1994; Bergstrom et al. 1995, 1998; Batchelor & Evans 2000; Kiipli & Kallaste 2006; E. Kiipli et al. 2006; Kiipli et al. 2007a, 2008). To reconstruct the volcanic history of a region, the stratigraphic distribution of numerous ash beds must be identified in different sections. Using well-preserved phenocrysts (sanidine, biotite, apatite, zircon, quartz, etc.) is advantageous compared to the bulk bentonite composition (Kiipli & Kallaste 2002; Kallaste & Kiipli 2006), although in some cases immobile trace elements can also serve as a good basis for correlation (Kiipli et al. 2001). Use of immobile trace elements is especially important in regions where metamorphism has destroyed primary magmatic phenocrysts, e.g. western Scandinavia. In this paper a range of immobile trace elements (Ti[O.sub.2], Zr, Nb, Th) determined by the X-ray fluorescence method is used to demonstrate correlations between sections. New and earlier studied sections (Kiipli & Kallaste 2002; Kallaste & Kiipli 2006) are used to trace the diachroneity of the boundary between the Rumba and Velise formations and to construct isopach maps to illustrate the distribution of ash beds.

STRATIGRAPHY

The stratigraphic position of the studied samples is in the Adavere Stage and the lower part of the Jaani Stage (Fig. 1). The lower part of the Adavere Stage consists of nodular limestones (Rumba Formation), while the upper part consists of shaly marlstones (Velise Formation). The carbonate content increases gradually in the lower part of the Jaani Stage (Mustjala Formation), where the rocks are represented by carbonate marlstones. Conodont and chitinozoan biozonation and scolecodont distribution in the Paatsalu section is described in O. Hints et al. (2006), while conodont zonation in the Viirelaid and Nassumaa sections is available in Kiipli et al. (2001). Telychian bentonites have also been correlated with graptolite zonation (Kiipli et al. 2007a). The boundary between the Adavere and Jaani stages is marked by the uppermost bentonite in a section of rocks with a high frequency of bentonites (Aaloe 1960). In terms of new bentonite stratigraphy, it is the level of the Kirikukula Bentonite (ID 457) (Kallaste & Kiipli 2006), lying very close to the lower boundary of the Pterospathodus a. amorphognathoides conodont Zone (Kiipli et al. 2001).

[FIGURE 1 OMITTED]

In terms of graptolite stratigraphy, the boundary between the Adavere and Jaani stages, which is marked by the Kirikukula Bentonite, is close to the spiralis-lapworthi boundary (Kiipli et al. 2007a). Bentonite names and ID numbers used herein are from Kallaste & Kiipli (2006). The same ID numbers and names were used also in Kiipli et al. (2007a, 2007c).

MATERIAL

In 2006, 16 clay-rich and feldspathic potential bentonite samples were collected from the Nassumaa-825 drill core. These include five bentonites that have been studied earlier by Kiipli et al. (2001) and Kiipli & Kallaste (2002). From the Orissaare-859 drill core 14 samples were collected, which have not been studied previously. The Nassumaa section is located in the southeastern part and Orissaare in the eastern end of Saaremaa Island (Fig. 2). Both cores are stored in the Geological Survey of Estonia.

[FIGURE 2 OMITTED]

In addition to the original material of this contribution, correlations based on the sanidine compositions from Kiipli & Kallaste (2002) and Kallaste & Kiipli (2006) were used for isopach schemes and study of the Rumba-Velise formations boundary.

LABORATORY METHODS

Standard X-ray fluorescence (XRF) techniques, using a VRA-30 at the Institute of Geology at Tallinn University of Technology, were employed for trace and major element analyses of sample material. Samples were powdered and mixed in a ball mill and small aliquots were used to make pressed powder pellets for analyses. Feldspathite powders required the addition of some drops of 5% MOWIOL solution. No binding material was used for pressing pellets of clay material. Empirical coefficients were used to account matrix corrections and overlapping X-ray spectral lines. Corrected total intensities of characteristic peaks were used to calibrate major element concentrations, while peak to background ratios were used for calibration of trace element concentrations. In a complicated range of the spectrum, with many overlapping peaks (e.g. Mo Ka to Pb L[beta]), the background was modelled and element intensities were calculated using a theoretical idealized spectrum. The measurements were calibrated using well characterized reference materials from France (Govindaraju 1995), Geological Survey of Japan, and Estonia (Kiipli et al. 2000; Kiipli 2005), and intercalibration samples of the International Association of Geoanalysts (IAG) (www.geoanalyst.org). Participation in IAG controlled proficiency testing over many years has verified the reliability and accuracy of the laboratory and its methods (Fig. 3).

IDENTIFICATION OF VOLCANIC ASH BEDS

Previous works (R Hints et al. 2006; Kiipli et al. 2008) have used X-ray dioractometry measurements to identify samples of volcanogenic origin. Good criteria are the occurrence of illite-smectite, authigenic K-feldspar, kaolinite and/or chlorite-smectite, together with low concentrations or absence of quartz. Bentonites can also be identified visually by colour variation and/or abundance of biotite flakes. Bentonite clays are often much softer than the host sediments. Feldspathites are similar to siltstones in appearance and have yellowish white colour. Herein we use XRF analyses for the identification of volcanic origin.

Pure terrigenous claystones are not common in Telychian sections of Estonia. Most rocks contain some carbonate material and few weight per cent of CaO. In contrast, volcanic ash layers typically contain <1 wt% CaO (see Kiipli et al. 2007c). Therefore low CaO concentrations constitute a preliminary indicator of the presence of volcanic ash layers in sections dominated by carbonate rock and marlstone. Higher abundance of carbonates and quartz in the host rock, as opposed to altered volcanic ashes, reduce the proportions of clay minerals, and consequently of the elements typical of clays and authigenic feldspar, such as [A1.sub.2][0.sub.3] and [K.sub.2]0. Therefore, the most useful monitor for bentonite identification is a binary chart of these two components. The samples from the Nassumaa and Orissaare cores were compared with altered volcanic ashes, terrigenous and carbonate rocks from Estonia and Latvia (Fig. 4). Terrigenous sediments are characterized by relatively low contents of [A1.sub.2][0.sub.3] (<20%) and [K.sub.2]0 (<7%), while altered volcanic ashes show higher concentrations of these elements. Most bentonites can be described as K-rich, containing 5-12% [K.sub.2]0 and 19-26% [A1.sub.2][0.sub.3]. Deep sea facies sediments of South Estonia and Latvia are characterized by kaolinite-rich bentonites and [K.sub.2]0 contents of 2-5%. Similar kaolinite-rich bentonites, often referred to as tonsteins, are known from coal formations (Bohor & Triplehorn 1993) and have very high [A1.sub.2][0.sub.3] contents (26-34%). Many altered volcanic ashes in Estonia and North America (Hay et al. 1988) contain >50% authigenic potassium feldspar (referred to as feldspathites; Kiipli et al. 2001, 2007b) and 12-16% [K.sub.2]0. Chlorite-smectite-rich bentonites, such as those found in the Pirgu Stage in Estonia (R. Hints et al. 2006), are particularly rich in MgO (6-15 wt%) and may be referred to as Mg-rich bentonites.

Twenty of the studied samples (Tables 1-3) lie in the fields of K-rich bentonites and feldspathites, one is a mixed feldspathite/terrigenous rock, and nine are in the field of terrigenous rocks. Some samples of the last group can contain a portion of volcanogenic material as far as fields of terrigenous rocks and mixed rocks are partly overlapping.

CORRELATION OF BENTONITES

To correlate bentonites from the Nassumaa and Orissaare sections with previously described sections, Zr and Ti[0.sub.2] concentrations were compared with the nearby Viirelaid and Paatsalu sections (Fig. 5) and provisional correlations were established. Then, using ratios of immobile elements (Table 4, Fig. 6), provisional correlations were checked. Geochemical correlation is based on the XRF analyses published in Kiipli et al. (2007c).

Five known bentonites occur in the Mustjala Formation (Kallaste & Kiipli 2006). Taking into consideration the stratigraphic position of the bentonites and comparing their compositions, the bentonites found at 55.3 and 58.8 m in the Orissaare section (Fig. 4) can be correlated with the Lusklint (ID 150) and Ohesaare (ID 210) bentonites, respectively, but not with the Ireviken (ID 127), Storbrut (ID 139), and Aizpute (ID 311) bentonites. The Aizpute Bentonite has notably higher Nb and Th and lower Sr contents; the Ireviken Bentonite has lower Sr and higher P205 contents; while the Storbrut Bentonite has lower Zr and Th contents. Sr contents vary in ID 150 and 210 from 108 to 236 ppm, in ID 127 from 69 to 94 ppm, and in ID 311 from 102 to 125 ppm. The P205 contents vary in ID 150 and 210 from 0.03 to 0.12%, in ID 127 from 0.14 to 0.42%, and in ID 311 from 0.12 to 0.18% (Kiipli et al. 2007c).

Five bentonites occur in the upper part of the Velise Formation, corresponding to the upper half of the Pterospathodus a. lithuanicus and the lowermost P. a. amorphognathoides conodont biozones (Kiipli et al. 2001) (Fig. 5). The bentonites at 201.8 and 199.7 m in the Nassumaa core correlated with the Ruhnu (ID 494) and Kirikukd1a (ID 457) bentonites by sanidine composition (Kiipli & Kallaste 2002). This is confirmed also by the results of geochemical analyses herein (Table 4 and Fig. 6).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

The compositions of bentonites at 200.7 m in the Nassumaa core and 69.9 m in the Orissaare core are very similar, and cluster near the data for the Viki (ID 475) and Kaugatuma (ID 480) bentonites (Fig. 6). The Viki and Kaugatuma bentonites may be distinguished by their contrasting sanidine compositions (Kallaste & Kiipli 2006). In addition, the Kaugatuma Bentonite has a considerable thickness (0.5-1.5 cm) only in cores of western Saaremaa. Consequently, the bentonites at 200.7 m in the Nassumaa core and at 69.9 m in the Orissaare core are positively correlated with the Viki Bentonite (ID 475).

The interval from the lower half of the P. a. lithuanicus conodont Biozone to the P. a. angulatus Biozone contains four significant bentonites (ID 518, 520, 521, 568). They are all geochemically similar and are characterized by high Ti[0.sub.2], Sr (182-320 ppm), and Ba (226-837 ppm) contents. Zr, Nb, and Th occur in lower concentrations. Bentonites ID 520 and ID 568 are characterized by elevated phosphorus (ID 520, 0.56-1.65%; ID 568, 0.05-0.36%) contents; ID 520 has also quite a high Y (59-80 ppm) content. From these data it can be suggested that the bentonites at 72.4 and 73.1 m in the Orissaare core are identical to ID 518 and ID 521. Meanwhile, the bentonites at 208.2 m in the Nassumaa core and at 76.8 m in the Orissaare core can be correlated with ID 568. The bentonite at 204.9 m in the Nassumaa core has similar geochemical features to both ID 518 and ID 521, but there is insufficient data to distinguish between the two.

In the section of the Velise Formation, equivalent to the Pterospathodus eopennatus ssp. n. 2 conodont Zone, using analogous arguments based on the composition, it is possible to correlate the bentonites at 219.4 m in the Nassumaa core and at 84.0 m in the Orissaare core with ID 696. A connection between ID 696 and the Nassumaa 219.4 m bentonite has also been suggested on the basis of sanidine composition (Kiipli & Kallaste 2002). Following similar arguments, and moving down the core, a number of other correlations between bentonites in the Korkkula-863, Viirelaid, and Paatsalu cores and bentonites from Orissaare and Nassumaa can be identified. The bentonites at 86.8 and 87.2 m in the Orissaare core can be positively correlated with ID 731 and ID 744. Meanwhile, the bentonite at 224.1 m in the Nassumaa core and at 87.2 m in the Orissaare core can be correlated with one another, as well as with ID 755. A positive correlation between the bentonite at 226.7 m in Nassumaa and ID 777 can also be drawn. The bentonite clay identified at 91.5 m in the Orissaare core does not correlate positively with any other samples studied here or in previous works.

At 93.9 m in the Orissaare core (in the Rumba Formation) there is a bentonite with anomalously high (3.7%) Ba content and a possible graphic correlation with the bentonite at 83.0 m in the Viirelaid core (ID 843) exists. The high Ba content is probably caused by authigenic accumulation of barite, although the source for authigenic accumulation of the element could be primary volcanic ash. The sample collected at 95.4 m in the Orissaare core can be confidently correlated with ID 851, which is also recognized as the Osmundsberg Bentonite (Bergstrom et al. 1998), found at several locations across Baltoscandia (Fig. 5).

DIACHRONEITY OF THE RUMBA-VELISE FORMATIONS BOUNDARY

Correlation of limestones of the Rumba Formation in Estonia with shales of the Degole Beds in Latvia has been demonstrated by the correlation of the Osmundsberg Bentonite through different facies zones (E. Kiipli et al. 2006). Einasto et al. (1972) argued that the boundary of the Rumba and Velise formations is synchronous in southwestern Estonia. Here we intend to show the diachronous nature of the Rumba-Velise boundary in Estonia (Fig. 5). The Rumba Formation consists of nodular limestones. The percentage of limestone nodules and marlstone interbeds varies, with the rock being in general more argillaceous in sections of western and southwestern Saaremaa and more carbonate in eastern sections. In the Korkkula, Nassumaa, and Orissaare sections there is a sharp boundary between nodular limestones of the Rumba Formation and homogeneous marlstones of the Velise Formation. The Viirelaid and Paatsalu sections include a 1.5-2 m thick transition interval with abundant limestone nodules in marlstone. Limestone nodules are abundant in the lower part of the Velise Formation also in the Varbla, Seliste, and Ikla sections (Einasto et al. 1972). Interestingly, by bentonites this transition interval of the Paatsalu section correlates confidently with the lower part of the Velise Formation in the Viirelaid core without limestones and with the even higher part of the Velise Formation in the Orissaare, Nassumaa, and Korkkula sections (Fig. 5). The Mustjala Bentonite (ID 795) in the Rumba Formation at 83.9 m in the Paatsalu core correlates with the 80.9 m level in the Viirelaid core (transition interval) and with 190.3 m in the Korkkula core, being without doubt within the lower part of the Velise Formation. Therefore, bentonite correlations show in detail the diachronous nature of the lithological boundary within a small distance of about 20-70 km.

THICKNESS DISTRIBUTION OF BENTONITES

When combined with stratigraphy, thickness distribution maps for volcanic ash beds are a useful tool for predicting the occurrence of particular ash beds. They can also be used to predict the geographic location of source volcanoes. The distribution patterns in Fig. 7 indicate that volcanic ash clouds arrived from the west (Viki, Kaugatuma, and Nassumaa bentonites), northwest

(bentonites ID 518, 520, 521, and 731) or southwest (Mustjala Bentonite). The distribution pattern of the Nurme Bentonite indicates a change in the wind direction during long-lasting eruption. Two ash cloud directions are indicated also on the composite isopach scheme of bentonites ID 518, 520, and 521. It is natural that all these eruptions had different ash cloud distributions and therefore two ash cloud movement directions are normal. Some other thickness distribution patterns of Silurian bentonites in the East Baltic and Scandinavia were published in Bergstrom et al. (1998), Kallaste & Kiipli (2006), E. Kiipli et al. (2006), Kiipli & Kallaste (2007), and Kiipli et al. (2007c, 2008).

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

CONCLUSIONS

Immobile trace elements Ti, Zr, Th, and Nb in combination with other geochemical signatures can be successfully used for correlation of bentonites in the Telychian of Estonia. Correlation potential of other trace elements needs to be studied carefully before using, because the mobility of many elements in the Earth's surface conditions can be expected from general geochemical considerations. Bentonite correlations show clear diachroneity of the Rumba-Velise formations boundary in Estonia. Thickness distribution patterns of bentonites indicate volcanic sources in the northwest, west or southwest.

ACKNOWLEDGEMENTS The authors are grateful to the referees C. J. Hetherington and K. Kirsimae for valuable comments and suggestions on the paper. This study is a contribution to the Estonian Science Foundation grants 6749 and 7605, target financing project 0332652s04, and IGCP503.

Received 22 October 2007, accepted 7 February 2008

REFERENCES

Aaloe, A. 1960. Some new research on the stratigraphy of the Silurian in Estonia. Eesti TA Geoloogia Instituudi uurimused, V, 123-141 [in Russian].

Batchelor, R. A. & Evans, J. 2000. Use of strontium isotope ratios and rare earth elements in apatite microphenocrysts for characterization and correlation of Silurian metabentonites: a Scandinavian case study. Norwegian Journal of Geology, 80, 3-8.

Batchelor, R. A. & Jeppsson, L. 1994. Late Llandovery bentonites from Gotland, Sweden, as chemostratigraphic markers. Journal of the Geological Society of London, 151,741-746.

Bergstrom, S. M., Huff, W. D., Kolata, D. R. & Bauert, H. 1995. Nomenclature, stratigraphy, chemical fingerprinting and areal distribution of some Middle Ordovician K-bentonites in Baltoscandia. GFF,117, 1-13.

Bergstrom, S. M., Huff, W. D. & Kolata, D. R 1998. The Lower Silurian Osmundsberg K-bentonite. Part I: stratigraphic position, distribution, and palaeogeographic significance. Geological Magazine, 135,1-13.

Bohor, B. F. & Triplehorn, D. M. 1993. Tonsteins: Altered Volcanic Ash Layers in Coal-Bearing Sequences. Geological Society of America, Boulder, Colo., 44 pp.

Einasto, R., Nestor, H., Kala, E. & Kajak, K. 1972. Correlation of the Upper Llandoverian sections in West Estonia. Eesti NSV Teaduste Akadeemia Toimetised, Keemia, Geoloogia, 21, 333-343 [in Russian].

Fisher, R. V. & Schmincke, H.-U. 1984. Pyroclastic Rocks. Springer-Verlag, Berlin, 472 pp.

Govindaraju, K. 1995. 1995 working values with confidence limits for twenty six CRPG, ANRT and IWG-GIT geostandards. Geostandards Newsletter, 19, Special Issue, 1-32.

Hay, R. L., Lee, M., Kolata, D., Matthews, J. C. & Morton, J. P. 1988. Episodic potassic diagenesis of Ordovician tuffs in the Mississipi Valley area. Geology, 16, 743-747.

Hints, O., Killing, M., Mannik, P. & Nestor, V. 2006. Frequency patterns of chitinozoans, scolecodonts and conodonts in the Upper Llandovery and Lower Wenlock of the Paat salu core, western Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 55, 128-155.

Hints, R., Kirsimae, K., Somelar, P., Kallaste, T. & Kiipli, T. 2006. Chloritization of Late Ordovician K-bentonites from the northern Baltic palaeobasin - influence from source material or diagenetic environment. Sedimentary Geology, 191, 55-66.

Kallaste, T. & Kiipli, T. 2006. New correlations of Telychian (Silurian) bentonites in Estonia. Proceedings of the Estonian Academy of Sciences, Geology, 55, 241-251.

Kiipli, E., Kiipli, T. & Kallaste, T. 2006. Identification of the O-bentonite in the deep shelf sections with implication on stratigraphy and lithofacies, East Baltic Silurian. GFF, 128,255-260.

Kiipli, T. 2005. Maavarade keemilise kvaliteedi andmekogu [Database of the chemical quality of mineral resources]. Eesti Geoloogiakeskuse aastaraamat 2004 (Kukk, M., ed.), pp. 34-37. EGK, Tallinn [in Estonian].

Kiipli, T. & Kallaste, T. 2002. Correlation of Telychian sections from shallow to deep sea facies in Estonia and Latvia based on the sanidine composition of bentonites. Proceedings of the Estonian Academy of Sciences, Geology, 51, 143-156.

Kiipli, T. & Kallaste, T. 2006. Wenlock and uppermost Llandovery bentonites as stratigraphic markers in Estonia, Latvia and Sweden. GFF,128, 139-146.

Kiipli, T. & Kallaste, T. 2007. Tuhapilvede modelleerimine Siluri vulkaaniliste kihtide leviku ja paksuste jargi. In Mudelid ja modelleerimine [Models and modelling] (Vers, E. & Amon, L., eds), pp. 24-30. Schola geologica III, ELUS, Tartu [in Estonian].

Kiipli, T., Batchelor, R. A., Bernal, J. P., Cowing, Ch., Hagel-Brunnstrom, M., Ingham, M. N., Johnson, D., Kivisilla, J., Knaack, Ch., Kump, P., Lozano, R., Michiels, D., Orlova, K., Pirrus, E., Rousseau, R. M., Ruzicka, J., Sandstrom, H. & Willis, J. P. 2000. Seven sedimentary rock reference samples from Estonia. Oil Shale, 17, 215-223.

Kiipli, T., Mannik, P., Batchelor, R. A., Kiipli, E., Kallaste, T. & Perens, H. 2001. Correlation of Telychian (Silurian) altered volcanic ash beds in Estonia, Sweden and Norway. Norwegian Joumal of Geology, 81, 179-194.

Kiipli, T., Kallaste, T., Kaljo, D. & Loydell, D. K. 2007a. Correlation of Telychian and lowermost Sheinwoodian K-bentonites with graptolite biozonation in the East Baltic area. Acta Palaeontologica Sinica, 46, 218-226.

Kiipli, T., Kiipli, E., Kallaste, T., Hints, R., Somelar, P. & Kirsimae, K. 2007b. Altered volcanic ash as an indicator of marine environment--example from the Ordovician Kinnekulle bed of Baltoscandia. Clays and Clay Minerals, 55,177-188.

Kiipli, T., Soesoo, A., Kallaste, T. & Kiipli, E. 2007c. Geochemistry of Telychian (Silurian) K-bentonites in Estonia and Latvia. Journal of Volcanology and Geothermal Research, doi:10.1016/j.jvolgeores.2007.11.005 [in press, available online].

Kiipli, T., Jeppsson, L., Kallaste, T. & Soderlund, U. 2008. Correlation of Silurian bentonites from Gotland and the eastern Baltic using sanidine phenocryst composition, and biostratigraphical consequences. Journal of the Geological Society, London, 165, 211-220.

Nestor, H. 1997. Silurian. In Geology and Mineral Resources of Estonia (Raukas, A. & Teedumae, A., eds), pp. 89-106. Estonian Academy Publishers, Tallinn.

Thorslund, P. 1945. Om bentonitlager i Sveriges Kambrosilur. GFF, 11, 171-178.

Tarmo Kiipli, Kiira Orlova, Enli Kiipli, and Toivo Kallaste

Institute of Geology at Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia; tarmo.kiipli@gi.ee
Table 1. XRF analyses of altered volcanic ash beds in the Nassumaa core

                                      Depth of the bed, m

                       199.7     200.7     201.8     204.9     208.2
Thickness, cm          3         4         4         0.10      2.50
ID                     457       475       494       521?      568

Content of major elements,
 Si[O.sub.2]           55.2      54.5      59.4      54.6      54.4
 Ti[O.sub.2]            0.766     0.863     0.345       1.30       1.01
 [A1.sub.2][O.sub.3]   16.9      25.0      23.1      17.9      22.4
 [Fe.sub.2][O.sub.3]    0.81      1.98      1.54      4.48      3.64
  total
 MnO                    0.014     0.006     0.005     0.006      0.008
 MgO                    1.05      3.16      2.89      1.33       2.52
 CaO                    5.08      0.95      0.41      1.10       0.84
 [K.sub.2]O            12.2       6.89      9.55     11.6        8.75
 [P.sub.2][O.sub.5]     0.17      0.07      0.04      0.27       0.27
 BaO                    0.46      0.02      0.01      0.03       0.02
 S                      0.22      0.12      0.10      1.76       0.09
 LOI 920 [degrees]C     4.30      5.96      3.98      4.20       4.20

Content of trace elements, ppm

 As                         10         6         6        17          9
 Bi                         <8        <8        <8        <8         <8
 Br                         <3        <3        <3        <3        3.20
 Ce                        120       184      <60         63         99
 Ga                          3        17        13         7         14
 La                        <40         55      <40       <40        <40
 Mo                         <3        <3        <3        <3         <3
 Nb                         13        37        38        18         22
 Pb                          9        10         5        21         16
 Rb                         59        83        91        64         82
 Se                        <4        <4        <4        <4         <4
 Sr                        208        92        59       225        159
 Th                         16        30        36        22         24
 T1                        <12       <12       <12       <12        <12
 U                           6         9       <8          7          7
 Y                          20        36         3        19         33
 Zr                        219       710       339       243        335

                                   Depth of the bed, m         Determin-
                       219.4     224.1     226.7     235.0     ation
Thickness, cm          2.50      4         2.50      8         limit
ID                     696       755       777?      851

Content of major elements,
 Si[O.sub.2]           56.3      53.0      55.4      61.4      0.07
 Ti[O.sub.2]            0.455     0.998     0.655     0.385     0.003
 [A1.sub.2][O.sub.3]   21.9      19.9      18.2      18.9      0.08
 [Fe.sub.2][O.sub.3]    4.04      8.52      5.90      1.29     0.004
  total
 MnO                    0.020     0.019     0.061     0.013      0.002
 MgO                    3.16      3.35      3.51      1.67       0.20
 CaO                    0.78      1.01      2.31      0.74       0.06
 [K.sub.2]O             7.72      7.07      7.79      13.0       0.004
 [P.sub.2][O.sub.5]     0.07      0.11      0.07      0.14       0.02
 BaO                    0.02      0.01      0.03      0.05       0.01
 S                      0.05      0.01      0.00      0.47       0.01
 LOI 920 [degrees]C     4.80      5.10      5.60      1.60       0.01

Content of trace elements, ppm

 As                         5         1         5         7          8
 Bi                        <8        <8        <8        <8          8
 Br                       2.2        <3        <3        <3          3
 Ce                        54       148       142       <60         60
 Ga                        21        19        19        15          3
 La                        30        70        39       <40         40
 Mo                        <3        <3        <3        <3          3
 Nb                        17        21        18        11          3
 Pb                         7        11         7         4          7
 Rb                       128        96       113        74          3
 Se                        <4        <4        <4        <4          4
 Sr                        72        77        81        75          3
 Th                        18        27        19        23          8
 T1                       <12       <12       <12       <12          12
 U                         <8        <8        <8        <8          8
 Y                         25        27        29         2          3
 Zr                       205       428       276       177         10

Table 2. XRF analyses of altered volcanic ash beds in the
Orissaare core

                                     Depth of the bed, m

                         55.3       58.8       69.9       72.4

Thickness, cm             4          6          3          1
ID                       150        210        475        518

Content of major elements,
Si[O.sub.2]               51.4       57.2       57.2       60.2
Ti[O.sub.2]                0.915      0.590      0.849      1.12
[A1.sub.2][O.sub.2]       23.6       25.6       22.7       19.0
[Fe.sub.2][O.sub.3]        4.63       1.12       1.92       1.16
 total
MnO                        0.006      0.005      0.007      0.012
MgO                        3.06       3.25       3.29       1.07
CaO                        0.97       0.82       1.04       1.17
[K.sub.2]O                 6.69       8.01       8.43      13.5
P[sub.2][O.sub.5]          0.06       0.05       0.06       0.28
BaO                        0.03       0.02       0.02       0.05
S                          2.47       0.13       0.17       0.25
LOI 920[degrees]C          7.90       5.00       5.00       1.50

Content of trace elements, ppm

As                        30         8          5          9
Bi                        <8         <8         <8         <8
Br                          2.0      <3         <3         <3
Ce                       <60        <60        <60        <60
Ga                        12         15         15         7
La                       <40        <40         30        <40
Mo                        <3         <3         <3         <3
Nb                        31         25         33         17
Pb                        36         11         5          9
Rb                        65         75         91         78
Se                        <4         <4         <4         <4
Sr                       236        137         85        270
Th                        34         26         25         18
T1                       <12        <12        <12        <12
U                         9          7          9          7
Y                         38         23         32         15
Zr                       570        459        626        240

                                     Depth of the bed, m

                         73.1       76.8       84.0       86.8

Thickness, cm          1          1.50       6          3
ID                     521        568        696        731

Content of major elements,

Si[O.sub.2]               58.1       56.6       57.3       57.3
Ti[O.sub.2]                1.12       1.00       0.454      0.450
[A1.sub.2][O.sub.2]       19.6       21.0       22.6       22.6
[Fe.sub.2][O.sub.3]        1.72       1.62       3.16       2.45
 total
MnO                        0.006      0.007      0.019      0.004
MgO                        1.53       2.07       3.20       3.73
CaO                        1.08       0.95       0.57       0.47
[K.sub.2]O                12.2       11.1        9.21       8.43
P[sub.2][O.sub.5]          0.22       0.36       0.08       0.07
BaO                        0.04       0.04       0.03       0.02
S                          0.88       0.84       0.13       0.06
LOI 920[degrees]C          2.80       3.20       3.60       4.60

Content of trace elements, ppm

As                        21         33         7          3
Bi                        <8         <8         <8         <8
Br                        <3         <3         <3         <3
Ce                       <60         88        <60        168
Ga                        9          11         20         23
La                        39        <40         39         75
Mo                        <3         <3         <3         <3
Nb                        18         18         17         34
Pb                        30         43         12         4
Rb                        69         66        126         95
Se                        <4         <4         <4         <4
Sr                       222        236         68         92
Th                        18         17         21         28
T1                       <12        <12        <12        <12
U                         9          9          <8         7
Y                         22         22         37         22
Zr                       309        290        268        392

                             Depth of the bed, m
                         87.2       87.6       93.9

Thickness, cm          1                 7   1
ID                     744             755   843?

Content of major elements,
Si[O.sub.2]               57.6       55.1       51.4
Ti[O.sub.2]                0.500      0.979      0.979
[A1.sub.2][O.sub.2]       21.0       22.6       15.3
[Fe.sub.2][O.sub.3]        3.32       3.37       0.61
 total
MnO                        0.009      0.002      0.008
MgO                        3.60       3.59       0.93
CaO                        0.64       0.54       6.90
[K.sub.2]O                 8.08       7.93      11.1
P[sub.2][O.sub.5]          0.07       0.09       0.06
BaO                        0.02       0.00       3.70
S                          0.08       0.13       1.17
LOI 920[degrees]C          4.40       5.30       5.30

Content of trace elements, ppm

As                        5          6          6
Bi                        <8         <8         <8
Br                        <3         <3         <3
Ce                       <60        250?       250?
Ga                        21         2          2
La                        36        <40        <40
Mo                        <3         <3         <3
Nb                        32         13         13
Pb                        4          4          4
Rb                       109         43         43
Se                        <4         <4         <4
Sr                        86        364        364
Th                        25         12         12
T1                       <12        <12        <12
U                         <8         <8         <8
Y                         10         9          9
Zr                       254        175        175

                             Depth of the bed, m
                         95.4     Determination limit

Thickness, cm             10
ID                       851

Content of major elements,

Si[O.sub.2]                61.1   0.07
Ti[O.sub.2]              0404  0  0.003
[A1.sub.2][O.sub.2]        18.3   0.08
[Fe.sub.2][O.sub.3]         1.18  0.004
 total
MnO                         0.014 0.002
MgO                         0.92  0.2
CaO                         0.45  0.06
[K.sub.2]O                 14.6   0.004
P[sub.2][O.sub.5]           0.22  0.02
BaO                         0.04  0.01
S                           0.30  0.01
LOI 920[degrees]C           0.60  0.01

Content of trace elements, ppm

As                        6          8
Bi                        <8         8
Br                        <3         3
Ce                       <60         60
Ga                        12         3
La                       <40         40
Mo                        <3         3
Nb                        8          3
Pb                        10         7
Rb                        65         3
Se                        <4         4
Sr                        62         3
Th                        18         8
T1                       <12         12
U                         6          8
Y                         5          3
Zr                       191         10

Table 3. XRF analyses of terrigenous claystones and mixed clays with
altered volcanic ashes in the Nassumaa and Orissaare cores

                                       Nassumaa, m

                            201.6    208.2    224.3    224.6

Thickness, cm                0.2      2.5       1        2
ID                           488      568

Content of major elements, %
Si[O.sub.2]                   51.7     52.8     53.6     56.7
Ti[O.sub.2]                  0.729    0.606    0.861    0.939
[A1.sub.2][O.sub.2]           14.7     16.4     15.2     16.2
[Fe.sub.2][O.sub.3] total     4.64     4.21     8.47     8.81
MnO                          0.050    0.037    0.063    0.045
MgO                           4.19     3.37     4.01     3.90
CaO                           7.98     6.59     4.16     1.26
[K.sub.2]O                    4.77     6.64     5.53     6.12
[P.sub.2][O.sub.5]            0.06     0.08     0.05     0.05
BaO                           0.03     0.03     0.04     0.04
S                             0.13     0.04     0.01     0.01
LOI 920[degrees]C            11.80     9.00     8.00     5.10

Content of trace elements, ppm
As                               5        7       12       10
Bi                              <8       <8       <8       <8
Br                             3.7       <3       <3       <3
Ce                              69       57       64       92
Ga                              14       14       18       18
La                              38      <40      <40       60
Mo                              <3       <3       <3       <3
Nb                              16       12       16       16
Pb                               2        9       10       10
Rb                             129      119      141      150
Se                              <4       <4       <4       <4
Sr                             106      127      103       69
Th                              11       10       17       15
T1                             <12      <12      <12      <12
U                               <8         6      <8       <8
Y                               21       25       25       27
Zr                             179      172      177      184

                                    Nassumaa, m

                            224.8    229.5    229.5

Thickness, cm                 2        5        5
ID

Content of major elements, %
Si[O.sub.2]                   55.8     42.6     51.2
Ti[O.sub.2]                  0.924    0.626    0.805
[A1.sub.2][O.sub.2]           16.2     12.7     15.0
[Fe.sub.2][O.sub.3] total     6.02     5.56     7.19
MnO                          0.051    0.129    0.094
MgO                           3.98     3.29     4.12
CaO                           3.90    15.86     6.37
[K.sub.2]O                    6.07     4.84     5.83
[P.sub.2][O.sub.5]            0.03     0.06     0.04
BaO                           0.04     0.03     0.03
S                             0.00     0.01     0.01
LOI 920[degrees]C             7.30    16.60     9.50

Content of trace elements, ppm
As                               4        5        3
Bi                              <8       <8       <8
Br                              <3       <3       <3
Ce                              70       51      <60
Ga                              17       12       19
La                              31      <40       37
Mo                              <3       <3       <3
Nb                              16       12       13
Pb                               5        5        7
Rb                             142       96      131
Se                              <4       <4       <4
Sr                             103      133       96
Th                              16       11       15
T1                             <12      <12      <12
U                               <8       <8       <8
Y                               28       22       20
Zr                             187      138      172

                              Orissaare, m
                                              Determination
                             78.9     91.5    limit

Thickness, cm                 1        5
ID

Content of major elements, %
Si[O.sub.2]                   48.2     55.9     0.07
Ti[O.sub.2]                  0.729    0.895    0.003
[A1.sub.2][O.sub.2]           14.4     16.5     0.08
[Fe.sub.2][O.sub.3] total     4.39     5.18    0.004
MnO                          0.049    0.040    0.002
MgO                           4.21     4.19      0.2
CaO                          11.37     4.00     0.06
[K.sub.2]O                    4.52     6.37    0.004
[P.sub.2][O.sub.5]            0.07     0.02     0.02
BaO                           0.04     0.03     0.01
S                             0.24     0.39     0.01
LOI 920[degrees]C            13.70     6.70     0.01

Content of trace elements, ppm
As                               4        4        8
Bi                              <8       <8        8
Br                              <3       <3        3
Ce                              46      <60       60
Ga                              17       19        3
La                              35      <40       40
Mo                              <3       <3        3
Nb                              14       16        3
Pb                               0        9        7
Rb                             120      137        3
Se                              <4       <4        4
Sr                             131       80        3
Th                              11       18        8
T1                             <12      <12       12
U                               <8        6        8
Y                               22       18        3
Zr                             161      192       10

Table 4. Geochemical comparison of bentonites from the Orissaare (O)
and Nassumaa (N) sections with the database of XRF analyses
(Kiipli et al. 2007c). ID, identification number of bentonites;
No., number of analyses; Avg, average; Std, standard deviation;
Ter, terrigenous sediments

ID     I          Zr/Ti[O.sub.2]    Nb/Ti[O.sub.2]    Th/Ti[O.sub.2]

127    No.               3                 3                 3
       Avg             0.047            0.0037            0.0036
       Std             0.007            0.0004            0.0007

139    No.               1                 1                 1
       Avg             0.036            0.0028            0.0024

150    No.               6                 6                 6
       Avg             0.054            0.0031            0.0036
       Std             0.010            0.0006            0.0004
       0-55.3          0.063            0.0035            0.0037
210    No.               6                 6                 4
       Avg             0.066            0.0034            0.0043
       Std             0.011            0.0005            0.0004
       0-58.8          0.078            0.0042            0.0044

311    No.               3                 3                 3
       Avg             0.061            0.0046            0.0057
       Std             0.005            0.0004            0.0001

457    No.               5                 5                 4
       Avg             0.034            0.0017            0.0021
       Std             0.005            0.0002            0.0001
       N-199.7         0.028            0.0017            0.0021

475    No.               9                 9                 6
       Avg             0.077            0.0044            0.0033
       Std             0.007            0.0005            0.0004
       N-200.7         0.080            0.0043            0.0034
       0-69.9          0.074            0.0039            0.0029

480    No.               3                 3                 3
       Avg             0.072            0.0043            0.0037
       Std             0.008            0.0002            0.0004

488    No.               6                 6                 5
       Avg             0.020            0.0012            0.0015
       Std             0.003            0.0001            0.0003

494    No.              10                10                 6
       Avg             0.097            0.0112            0.0106
       Std             0.006            0.0008            0.0012
       N-201.8         0.098            0.0109            0.0108

518    No.               5                 5                 4
       Avg             0.025            0.0015            0.0017
       Std             0.004            0.0001            0.0001
       0-72.4          0.021            0.0015            0.0016

520    No.               5                 5                 3
       Avg             0.029            0.0016            0.0022
       Std             0.003            0.0001            0.0006

521    No.               4                 4                 3
       Avg             0.024            0.0015            0.0016
       Std             0.004            0.0001            0.0002
       N-204.9         0.019            0.0014            0.0017
       0-73.1          0.028            0.0016            0.0016

568    No.               5                 5                 4
       Avg             0.028            0.0016            0.0018
       Std             0.004            0.0004            0.0004
       N-208.2         0.033            0.0022            0.0023
       0-76.8          0.029            0.0018            0.0017

658    No.               1                 1                 1
       Avg             0.094            0.0071            0.0069

693    No.               1                 1                 1
       Avg             0.041            0.0045            0.0045

696    No.              10                10                 7
       Avg             0.055            0.0033            0.0042
       Std             0.012            0.0007            0.0011
       N-219.4         0.046            0.0037            0.0040
       0-84.0          0.060            0.0038            0.0048

705    No.               1                 1                 1
       Avg             0.092            0.0081            0.0069

719    No.               5                 5                 3
       Avg             0.066            0.0036            0.0042
       Std             0.012            0.0007            0.0009

720    No.               1                 1                 1
       Avg             0.115            0.0096            0.0257

722    No.               1                 1                 1
       Avg             0.025            0.0018            0.0023

731    No.              11                11                 8
       Avg             0.085            0.0078            0.0071
       Std             0.010            0.0008            0.0007
       0-86.8          0.087            0.0075            0.0061

744    No.               7                 7                 6
       Avg             0.059            0.0075            0.0080
       Std             0.010            0.0013            0.0020
       0-87.2          0.051            0.0065            0.0049

750    No.               1                 1                 1
       Avg             0.035            0.0031            0.0050

755    No.               8                 8                 6
       Avg             0.048            0.0023            0.0029
       Std             0.007            0.0004            0.0004
       N-224.1         0.043            0.0021            0.0027
       0-87.6          0.051            0.0024            0.0027

772    No.               6                 6                 5
       Avg             0.056            0.0038            0.0066
       Std             0.012            0.0007            0.0016

773    No.               1                 1                 1
       Avg             0.065            0.0032            0.0059

774    No.               1                 1                 1
       Avg             0.095            0.0055            0.0042

776    No.               4                 4                 4
       Avg             0.101            0.0095            0.0208
       Std             0.021            0.0035            0.0041

777    No.               4                 4                 4
       Avg             0.045            0.0028            0.0031
       Std             0.008            0.0005            0.0003
       N-226.7         0.043            0.0027            0.0030

788    No.               1                 1                 1
       Avg             0.058            0.0037            0.0029

795    No.               3                 3                 3
       Avg             0.086            0.0049            0.0067
       Std             0.014            0.0020            0.0007

818    No.               1                 1                 1
       Avg             0.035            0.0021            0.0000

823    No.               3                 3                 2
       Avg             0.101            0.0053            0.0048
       Std             0.009            0.0007            0.0017

843    No.               2                 2                 2
       Avg             0.034            0.0032            0.0024
       Std             0.004            0.0005            0.0001
       0-93.9          0.037            0.0028            0.0025

851    No.              11                11                 8
       Avg             0.048            0.0023            0.0049
       Std             0.004            0.0005            0.0008
       N-235.0         0.048            0.0033            0.0061
       0-95.4          0.048            0.0021            0.0045

870    No.               1                 1                 1
       Avg             0.013            0.0008            0.0005

880    No.               2                 2                 2
       Avg             0.026            0.0015            0.0021
       Std             0.008            0.0005            0.0010

Ter    No.               8                 8                 8
       Avg             0.022            0.0018            0.0018
       Std             0.003            0.0001            0.0002
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