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
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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