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Geochemical heterogeneity of Estonian graptolite argillite.

1. Introduction

The Estonian graptolite argillite (GA), Tremadoc in age, is distributed in northern Estonia and on Vormsi and Hiiumaa islands. It belongs to the Turisalu Formation and is overlain by glauconitic sandstones and clays of the Varangu Stage and underlain by the phosphatic quartzose sandstone of the Kallavere Formation [1]. The GA is an argillaceous rock enriched with organic matter [2] and is characterized by high concentrations of a number of trace elements, including U, V and Mo. The thickness of GA reaches 7.4 m in NW Estonia and decreases towards the east and south. On a regional scale, GA belongs to the wide but patchy belt of Middle Cambrian to Lower Ordovician black shales extending from Lake Onega district in the east to the Caledonian front, Oslo region and Jutland Peninsula in the west [3-6].

There are numerous studies conducted on various metalliferous black shale/oil shale deposits worldwide--black shale deposits in North America [7-12], China [13, 14], central Europe [15], and alum shale in Scandinavia [3, 16-20]--focusing on the general characteristics and different aspects of metallogenesis in those assemblages. Also, a series of investigations have been targeted on the general geochemistry and trace element distribution of Estonian GA [21-30].

The metalliferous nature of GA was well known already in the first half of the last century. A more systematic picture of GA outside its outcrop area near the Baltic Klint, however, was gathered thanks to the extensive geological mapping of basement, drilling and geochemical investigations, which started in the 1950s and were conducted by the Geological Survey of Estonia. The vast amount of detailed information on the GA lithology and geochemistry was collected during the prospecting of Estonian phosphorite resources, e.g. [23, 31, 32]. The previous investigations have allowed depicting general trends of trace element enrichment and lateral distributions within GA, demonstrating at the same time high trace metal heterogeneity of those deposits [26, 28, 29]. Still, relatively little is known about the source of metals and the mechanism that caused metal enrichment in many black shale deposits worldwide, including GA. Although several investigations have been conducted during the past decades [25-30], the origin of metals is still unclear, as why their content is so heterogeneous laterally and also vertically through the GA complex.

Based on previous geochemical investigations [26] three geochemical zones have been distinguished in Estonian GA: Western, Central and Eastern zones (Fig. 1). The zones differ mainly in concentration of metals which are characteristic of GA--Mo, V, U. However, based on the present study it will be shown that the distribution of metals in GA has a more complex pattern. This paper describes the vertical bed-to-bed variation of metals, with emphasis on two vertical cross-sections, and discusses some possible critical factors that may stand behind the trace metal enrichment and heterogeneity in those complexes. Samples for the study were collected from Pakerort cliff on Pakri Peninsula, NW Estonia and Saka cliff, NE Estonia (Fig. 1), selected to represent GA complex in different geochemical zones. According to biostratigraphic studies GA in those localities does not represent strictly coeval sedimentation: GA from Western Estonia is assigned to the Pakerort Stage, whereas GA within the Eastern Zone belongs to the younger Varangu Stage [33, 34].

2. Material and methods

Two outcrops, Pakri and Saka, were sampled at 20 cm intervals for geochemical analysis. Twenty-one fresh GA samples from Pakri and nine samples from Saka were collected from the outcrop sections of 4.2 m and 1.8 m, respectively. The weight of samples was approximately 2 kg. The samples were cleaned, dried, crushed and homogenized for chemical analysis. The sample powders were analyzed for major and trace element composition, including rare earth elements, in order to determine the geochemical changes across the section and general rock composition. Geochemical analysis was performed using X-ray fluorescence (XRF) and ICPMS analysis.

XRF analysis was conducted at the Institute of Geology, Tallinn University of Technology (TUT), with an S4 Pioneer Spectrometer (Bruker AXS GmbH, Germany), using an X-ray tube with a rhodium anode, which operated with a power of 3 kW. The samples were measured with a manufacturer's standard as MultiRes modification (pre-calibrated standardless method). The in-house standard ES-2 ("Dictyonema Shale") was used as reference material [34]. Loss on ignition (LOI) was determined from 1 g of sample material at 500 [degrees]C and 920 [degrees]C. ICP-MS analysis was conducted at the Institute of Geology, TUT. Rare earth elements of Pakri samples were determined from solutions which were prepared following the nitric, hydrofluoric, hydrochloric and boric acids digestion of a 0.250 g pulverized sample in an Anton Paar MW3000 microwave oven. A set of samples from Pakri and Saka were additionally re-analyzed for trace elements, including rare earths, at ACMELABS in Canada.

Mineralogical analysis of selected whole rock powdered samples was conducted using an X-ray diffractometry apparatus (HZG4 diffractometer) at the Institute of Geology, TUT. XRD analysis was performed using a Fe-filtered Co radiation (35 kV and 25 mA) and scintillation detector. The range from 5-45[degrees]2[THETA] was scanned with a step of 0.04[degrees]2[THETA]. For selected samples complementary scanning electron microscope (SEM) analysis was used. SEM examination of uncoated rough and flat unpolished GA samples was carried out at the Institute of Geology, TUT, with a Zeiss EVO MA15 scanning electron microscope.

3. Mineralogy of graptolite argillite

GA is a fine-grained kerogen-rich siliceous deposit characterized by high content of organic matter (15-20%) and pyrite (2.4-6.0%) [2], and very low thermal maturity. The mineral assemblage of GA is according to previous studies dominated by K-feldspars, quartz and clay minerals [35, 36]. In the lateral as well as vertical dimension the contents of major rock-forming minerals show slight but pronounced variation patterns [35, 37, 36]. The average content of quartz in GA gradually rises eastward with the corresponding clay mineral decrease. In NE Estonia, the argillite complex is intercalated with numerous quartzose silt beds [30]. From authigenic sulfides, the occurrence of pyrite, marcasite, sphalerite and galena has been documented. In outcrops and drill cores secondary gypsum and jarosite commonly appear. In general, a higher degree of sulfide mineralization within GA is associated with the occurrence of silt interbeds. Those interbeds might also host a higher amount of other minor authigenic compounds typical for GA--phosphates (mainly apatite as biogenic detritus and nodules), carbonates (calcite and dolomite as cement and concretions), barite and glauconite. Besides the highly resistant terrigenic accessory phases, considerable abundance of micas in GA beds has been documented [35, 37].

Detailed mineralogical study is beyond the scope of the present paper. However, in order to record general mineralogical outline, XRD analysis of selected GA samples from the Pakri outcrop was performed. The study confirmed the presence of K-feldspar (sanidine), illite (illite-smectite, micas), quartz, pyrite, marcasite, apatite, calcite, dolomite, galena and chlorite. The analysis with SEM revealed high micrometer-scale morphological heterogeneity in the examined samples. The dominance of finely disseminated microcrystalline euhedral K-feldspar and quartz in argillite suggests that these minerals in GA are commonly authigenic in origin. The multistage development of syngenetic-diagenetic mineral assemblages and importance of redistribution processes in GA are suggested by the occurrence of a high variety of pyrite crystal forms within the argillite matrix as well as in sulfide enriched interbeds.

4. Results and discussion on the geochemistry of the Estonian graptolite argillite

Detailed vertical geochemical heterogeneity in the GA has not been studied previously. There is little understanding of the scale of heterogeneity and distribution pattern of elements. Moreover, detailed lateral geochemical changes across the GA unit are unknown. As an example of elemental distribution, V, Mo and Pb within the Estonian GA unit are displayed in Figure 2. The initial data were selected from the database of the Geological Survey of Estonia. These elemental concentration data represent the calculated average concentration in the GA in the drill core. The central and western parts of the Eastern Zone show the highest concentrations for V and Mo (Figs. 2, 1). Generally, it can be concluded that the concentration of most of the metals is relatively low in the Central Zone (Figs. 2, 1). Pb shows the highest concentrations on Hiiumaa Island. It must be emphasized that the available data is relatively unevenly distributed, especially the southern margin of the GA bed. Therefore, geochemical generalizations of this kind are informative but must be taken with precaution. More drilling material and studies of the vertical geochemical change of elements in GA are needed to define spatial geochemical patterns.

4.1. Major elements

The bed-to-bed study performed on geochemical variation from Saka and Pakri sections show that major elements vary relatively little across the examined GA sequences (Table 1). Analyses indicate that the GA assemblage is siliceous, high-K, Mn-poor and with variable Fe and S contents.

The Si[O.sub.2] abundance in examined GA sections varies from 45.74 to 55.11 wt% and shows a general increase towards the upper part of the GA complex. The observed distribution pattern agrees with previously described lithological changes--general increase of the silt/clay ratio from bottom to top of the beds in Estonian GA sequences [37, 36]. Besides, there is an inverse correlation between LOI 500 [degrees]C (reflecting organic matter content in GA) and Si[O.sub.2]. The [Al.sub.2][O.sub.3] content varies between 10.9 and 14.49 wt% and its average concentration is somewhat higher in GA from the Pakri locality. Titanium behavior shows a strong correlation with aluminum suggesting a possible detrital origin. The distinct feature of the Estonian GA is its elevated potassium content, in Pakri and Saka GA sequences [K.sub.2]O ranges from 6.59 to 8.44 wt%. The high potassium content is likely connected with the abundance of authigenic K-feldspar in those beds, thus differentiating Estonian GAs from the Scandinavian alum shale, where clay minerals occur as the dominant K-rich phases [38]. Pronounced potassium enrichment is also evident when the detected chemical composition of GA is compared with the compositions of widely used standard shale compilations such as PAAS (Post Archaean Australian Shale) [39], and NASC (North American Shale Composite) [40] (Fig. 3). On the other hand, a number of major element compounds, such as MnO, [Na.sub.2]O, CaO, MgO, appear to be considerably depleted with respect to the "standard shale" composition. The content of all those elements in the studied GA sequences is consistently well below 1.5 wt%.

The invariably low manganese content of Cambrian-Tremadoc black shales of the Baltoscandian region was interpreted by Wilde et al. [10] as an indicator of persistently euxinic environment during accumulation of the black shale complexes. Typically for the organic-rich deposits formed under oxygen deficient environment, the Estonian GA suggests efficient sequestration of sulfur and iron. The content of these elements is, however, highly variable in different samples investigated. The content of [Fe.sub.2][O.sub.3] in the examined samples varied between 3.79 and 6.08 wt%. The sulfur concentration changed from 1.34 to 4 wt%. The strong correlation between the abundances of sulfur and iron in the Pakri GA sequence indicates that most of the sulfur is incorporated into iron sulfides rather than into organic matter. In the Saka section the correlation between the behaviors of sulfur and iron is less apparent, partly probably due to formation of secondary sulfates and phosphates. [P.sub.2][O.sub.5] and CaO, whose abundance in GA is generally low, are mainly included in apatite, as suggested by the covariance of those elements in the GA samples. Nevertheless, the detailed variance patterns of phosphorus in Saka and Pakri sequences reveal that on the background of generally monotonous phosphorus content some GA intervals (e.g. Saka2, Saka9, Pakri17) present anomalously high concentrations of [P.sub.2][O.sub.5]. Elevated phosphorus values might be due to the higher level of mixing with phosphatic detritus, suggested by the considerable abundance of phosphatic bioclastic fragments in these GA levels or due to the formation of diagenetic apatite.

If the two GA sequences under study are compared on the basis of major element composition, differences appear to be moderate--the Pakri samples have a slightly higher content of [K.sub.2]O, [Al.sub.2][O.sub.3], Ti[O.sub.2] and MgO and a lower content of CaO and [P.sub.2][O.sub.5]. In general, the relatively homogeneous major element distribution gives limited clues for predicting the highly inhomogeneous trace element enrichment patterns and for unraveling the processes behind enrichment.

4.2. Trace elements

Trace metal enrichment in black shales is mostly explained by two alternative theories: 1) synsedimentary sequestration of metals under oxygen-deficient conditions from marine water, e.g. [41, 12, 20], or 2) flushing of the sediments by metal-enriched syngenetic brines or contemporaneous exhalation of such brines into marine basin, e.g. [42, 14, 43, 25, 30]. However, these theories are challenged by works that underline the influence of source rocks and particulate precursor material on the final character of metal enrichment in black shales, e.g. [44], or the crucial role of diagenetic redistribution processes induced by late diagenetic brines, e.g. [8, 45].

In general, U-Mo-V-Pb enriched trace metal association with sporadically elevated concentrations of some other trace elements was detected in GA from Saka and Pakri sections (Table 2). For assessing the degree of enrichment of particular trace metals in GA, the detected average trace element abundances were compared with average shale and black shale standard compilations. With respect to PAAS and NASC values the GA appears to be extremely enriched in U and V (Fig. 3). For example, the average U concentration in the Saka section (267 ppm) is a hundred times higher than the corresponding values for NASC. There is a nine-fold difference in V concentration between NASC and Saka GA section (average 1190 ppm). If compared with the minimum enrichment values (m.e.v.) for metalliferous black shales (suggested by Vine and Tourtelot [7] on the basis of generalized data of numerous North-American black shales), the studied samples and the Estonian GA in general could be considered enriched with U (m.e.v. 30 ppm), Mo (m.e.v. 200 ppm), V (m.e.v. 1000 ppm), Pb (m.e.v. 100 ppm) and Co (m.e.v. 30 ppm; only in Saka samples) [28].

All previously listed enriched trace metals of GA as well as other abundant trace elements, like As, Sb, Ni, Cu, Re, belong to the group of redox sensitive and/or stable sulfide-forming metals and might undergo considerable partitioning in marine geochemical and biochemical cycles. As indicated by the studies of trace elements in modern marine environments, e.g. [46-48], the redox sensitive elements mostly occur as soluble species under oxidizing conditions. Under the oxygen-depleted conditions, however, the redox sensitive elements are typically present as insoluble species (metal-organic complexes, sulfides, metal oxyhydrates) and thus tend to sequester into sediments. The whole metal trapping process is strongly linked with organic matter breakdown and sulfate reduction processes, which inhibit the crystallization of sulfides. In addition to the redox sensitive trace elements, other elements like Fe and Mn found commonly enriched in black shales, are essential recyclers in redox partitioning in marine systems [49]. Consequently, based on numerous comparative studies of trace element accumulation in modern and ancient organic rich sediments, e.g. [50, 51], it has been suggested that oxygen availability in sedimentary environment could have had sole control over development of enriched trace metal associations in different black shales, e.g. [12].

The performed geochemical investigations revealed that the studied sequences present pronounced vertical variations in U, V, Mo and Zn concentrations (Fig. 4). The listed trace elements do not show completely matching variance patterns and the maximum (and minimum) enrichment intervals of different components mostly do not overlap. In case of the Pakri GA sequence one can separate about 1.3 m thick lower part, which is enriched with some trace metals like Mo, U and Sb, and also contains more organic matter as indicated by higher LOI 500 [degrees]C values. While Mo is gradually decreasing towards the upper part of the Pakri sequence, U and V contents are somewhat more erratic. The thinner GA complex from Saka, which on average contains more Mo, U and V than the Pakri GA, is also characterized by the larger variance of those elements. In Saka samples, no clear vertical distribution trends of Mo and U can be followed, the concentrations fluctuate on a large scale and very high values alternate with low ones. For example, in samples Saka1 and Saka4 the Mo content is 1143 and 1843 ppm, respectively, while between these samples it only varies between 85 and 97 ppm. In general, Mo and U contents in the Saka section show quite a strong positive covariance with organic matter content (LOI 500 [degrees]C). The sample Saka4, which presents anomalously high values of these elements, also yielded the highest LOI 500 [degrees]C value. These results agree with the observation that the contents of V, U and Mo in black shales typically correlate with the abundance of organic matter [7], likely indicating early fixation via metal-organic complexes. However, in case of V, which shows considerably high values throughout both studied GA sequences, the correlation with organic matter is less expressed.

The average content of Pb is similar in both investigated sections and its vertical distribution is rather homogeneous. Lead shows a positive covariance with elements presumably related with sulfides--[Fe.sub.2][O.sub.3], S, Cu, Se, Ag, Hg in Pakri samples, while in Saka there is a positive correlation with S and Ta, and a negative one with Cu, Li, Re, Sn. Zn generally demonstrates an opposite trend to internally enriched elements such as U, V, Mo. Its abundance is two times higher in Pakri samples compared to Saka ones. However, the elevated concentrations of Zn in the Pakri section (up to 761 ppm in Pakri4) are limited to the well-defined interval 60-120 cm from the bottom, whereas the rest of the sequence is characterized by a monotonous Zn concentration near 40-60 ppm. In the Saka section the content of Zn is very low in the lower part of the section, but shows a general increase toward the upper part of the complex. The pronounced positive covariance of Cd with Zn in the studied sequences likely indicates a coeval trapping of those phases during sphalerite formation.

U positive covariance with [P.sub.2][O.sub.5] was not detected in the samples under study. Trace metal partitioning into phosphates has been suggested by some studies [52] as a process responsible for the higher general concentration of U in the GA of NE Estonia.

In general, the dominance of common marine redox sensitive elements among enriched metals in GA favors syngenetic enrichment as the major process of trace metal sequestration. On the other hand, the remarkably high concentration of enriched elements in GA and the variable covariance patterns imply that element sequestration solely from seawater due to Eh gradients is likely an insufficient model for explaining the observed large-scale trace metal heterogeneity in GA. Furthermore, the current data (Tables 2, 3) as well as previous studies [2] indicate that besides the elements, for which partitioning in marine systems is well known, GA sporadically presents elevated levels of some minor elements, e.g. PGE and W, characterized by generally very low abundance in average crust and modern marine sediments. The accumulation of such minor compounds in GA underlines the role of internal input of metals into the sedimentary or diagenetic environment.

The closeness of probable denudation areas (the peneplain of Proterozoic crystalline rocks in Southern Finland) to the sedimentary setting where GA accumulated hints that the trace elemental composition of sea water in these areas likely bore a distinct terrestrial signature, similarly to recent coastal marine environments [49]. Moreover, recent studies in Caledonian Nappe complexes, e.g. [53], suggest the existence of subduction zone related volcanic arc complexes within the Iapetus Ocean near the western border of the Baltica paleocontinent in the Late Cambrian and Tremadoc. The associated volcanic activity in these areas could supply overlying waters with extra trace metal budgets and modify regional marine trace metal signals enhancing, for example, Zn and V content of marine water. Then again, the likely introduction of the particulate volcanic matter to the sedimentary basin during the times of GA formation is suggested by clay mineral studies. According to Utsal et al. [35] the widespread occurrence of authigenic illite-smectite in GA indicates that at least 10% of its primary sedimentary matter was made up of volcanic ash.

The differences in trace element composition of GA might thus in some instances reflect variations in source material fluxes. First of all this relates to non-reactive elements with negligible solubility in surface environments transported to the sedimentary basin mainly in the composition of terrigenic (volcanic) matter such as residual heavy minerals, secondary weathering products or volcanic ash. According to Vine and Tourtelot [7], the detrital fraction of most black shales is characterized by the elements Al, Ti, Zr, Ga, Sc, and may also commonly include Be, B, Ba, Na, K, Mg, and Fe. Additional elements generally considered insensitive to secondary processes include Nb, Y, Th, Ta, Hf, and the REEs [39].

On the La-Al and La-Ti diagrams (Figs. 5A, 5B) the distribution of Al and Ti shows a similar pattern with respect to the lanthanum behavior. The Pakri samples with higher alumina and silica values and somewhat higher Ti content have enhanced La values as compared to Saka samples. The covariance of La with typical detrital compounds suggests that La may be dominantly bounded by detrital phases. However, the abnormally high La content detected in three phosphorus-rich samples may suggest a possible synsedimentary incorporation into the biogenic detritus or diagenetic mobility of La. Be and Ni abundances in the Pakri section demonstrate a two-line positive covariance trend (Fig. 5C). Such a distribution pattern of two elements with generally different geochemical behavior in surface systems might reflect the terrigenic (volcanogenic) flux into the sedimentary environment from a distinct source during the initial period of accumulation of the GA or specific sedimentary conditions supporting Ni enrichment. The terrigenic flux controlled abundance is suggested also for Li and Mg (Fig. 5D). Both elements show a very well defined positive correlation, suggesting that Li and Mg are likely bonded into the crystal structure of micas and/or clay minerals. Figures 5E and 5F present the relations of Sc, Th, and La, widely exploited for discriminating different magmatic rock types and settings. Numbers of studies have employed these variations to track possible precursor rocks of ancient shale and black shale complexes [39, 54]. On the Th-Sc graph the Pakri and Saka samples present anomalously low Sc and high Th/Sc content (Fig. 5E), thus suggesting a generally felsic upper crustal precursor for GA. The La/Th ratios of the analyzed GA samples demonstrate considerably higher scattering. As mentioned above, however, the enhanced La values in phosphorus-rich samples suggest that precursor rock signal had been in some cases evidently obscured by the synsedimentary incorporation or posterior redistribution of La.

In general, the clustering of non-reactive trace element data into the two fields may suggest that two different dominant source areas were involved in the supply of detrital material to the localities where organic-rich muds once accumulated.

4.3. Rare earth element variations

The REE patterns recorded for post-Archaean shales (PAAS) show striking similarity worldwide: they are light REE enriched, with a negative Eu anomaly and relatively flat heavy REEs [55, 39]. Samples from Pakri show chondrite-normalized (CN) REE patterns (Fig. 6C) generally similar to those recorded for PAAS, being considerably enriched in light rare earth elements (LREEs) with respect to heavy rare earth elements (HREEs). The main difference from the average shale compilations appears in content of MREEs (Fig. 6B). Like PAAS, all the studied samples exhibit negative Eu anomaly. The [La.sub.CN]/[Yb.sub.CN] ratio ranges from 6.65 to 10.26, staying thus well below the upper crust's [La.sub.CN]/[Yb.sub.CN] ratio. The [Gd.sub.CN]/[Yb.sub.CN] ratio varies from 1.09 to 2.22 with an average of 1.44 which is close to the PAAS value. The PAAS-normalized REE patterns of the examined GA samples show generally flat shape (Figs. 6A, 6B). In respect of the considerably monotonous REE variations, three samples from the Pakri locality exhibit distinct behavior. Pakri21 and Pakri14 have similar REE fractionation patterns with a somewhat elevated content of MREEs compared to PAAS. A unique hat-shape REE shale-normalized pattern was recorded for Pakri17 sample, which also presents a clearly elevated absolute REE concentration and strong MREEs enrichment. Compared to the Pakri sequence the REE patterns for Saka samples show higher fractionation and variation in the content of REEs (Figs. 6A, 6C). The [La.sub.CN]/[Yb.sub.CN] ratio is similar to that in Pakri samples, except in Sakal and Saka4 where it reaches 15.56 and 14.27, respectively. The [Gd.sub.CN]/[Yb.sub.CN] ratios show high variation from 0.66 to 2.76, being the highest in samples Saka2 and Saka3. The MREE pattern shows higher variation than in Pakri samples. The PAAS-normalized REE patterns of Saka1, Saka4, Saka5, and Saka6 show low REE absolute abundances, but are characterized by distinctive concave shape patterns with considerably enriched HREEs (Tm-Yb) with respect to depleted MREEs (Ce-Er). Remarkably, these samples have the lowest content of [Fe.sub.2][O.sub.3] and the highest contents of Mo, U and V (though high contents of these trace elements also occur in other samples). The hat-shaped (similar to that of Pakri17), MREE enriched patterns characterize Saka2 and Saka3 samples. The REE patterns of samples Saka7, Saka8, and Saka9 are more flat-shaped, similar to a typical Pakri pattern.

The observed large-scale variations in REE patterns--the encounter of normal flat shape as well as hat and concave like patterns--could be explained by variations in detrital input, e.g. variations in accessory mineral associations. However, alternatively it might point to the possibility that in most samples of the Saka sequence and in some intervals of Pakri the source rock inherited REE signals have been masked or obscured by the synsedimentary, diagenetic, hydrothermal or weathering induced redistribution enrichment of REEs. The recent studies of black shales have indicated that authigenic phases such as sulfides, phosphates and carbonates as well as organic matter may host elevated REEs and their presence might influence the absolute abundances of REEs as well as the fractionation patterns, e.g. [56]. Cruse et al. [57] interpreted the intermittent occurrence of hat and concave shape shale-normalized REE patterns in authigenic phosphate-rich and low-phosphate black shales as the evidence of an early diagenetic redistribution of REEs formed as the result of a preferential uptake of MREE in apatite and simultaneous depletion of phosphate-poor host shale beds. A similar enrichment process could be hypothesized for the MREE enriched samples of Saka and Pakri GA, all characterized by elevated phosphorus content compared to the rest of the samples under study. This agrees with high REE values detected by SEM analysis of authigenic as well as bioclastic phosphates in the studied sequences. Lev et al. [58] demonstrated the importance of post-/syn-depositional mineralizing fluid induced disturbance in REE-systems together with redistribution of U in black shales. Consequently, the encountered REE fractionation patterns could theoretically indicate also the influence of short-term low temperature brines. In case of GA the possible influence of deep source brines on the formation of its mineral assemblage has been suggested previously by sulfur isotope studies of pyrite [25]. However, the influence of deep brines on the Estonian Lower Paleozoic sedimentary assemblage is problematic as the whole complex is thermally almost unaltered. On the other hand, Somelar et al. (2010) [59] suggested intrusion of low temperature K-rich brines as the mechanism behind the illitization of Estonian Ordovician K-bentonites, pointing to the possible wide-scale influence of alkaline brines on the region in the Late Silurian.

Nevertheless, despite the lack of knowledge of the precise formation mechanism of the observed variability of REEs, it might suggest REE mobility in sedimentary or diagenetic environments. One could also speculate that the co-appearance of MREE depleted patterns and enhanced U, V and Mo abundances in GA from the Saka outcrop might indicate that those enriched elements were affected by the same redistribution processes which resulted in the formation of MREE depleted patterns.

5. Conclusions

The studies of two vertical sequences of graptolite argillite (GA) show the existence of pronounced fine-scale trace metal variability in GA. The examined samples were detected to be enriched in U, V, Mo and Pb with respect to average black shales, the obtained results thus agreeing with previously published data on the geochemistry of GA. The content of enriched elements was, however, recorded to change greatly over the examined sequences, suggesting a notably more complex nature of trace metal distribution in GA than previously assumed. Redox sensitive metals U and Mo, and also V to a lesser extent, showed loose covariance with organic matter content (LOI 500 [degrees]C), apparently indicating their trapping mainly via organic matter tied species, and the enrichment primary linked to organic matter sequestration. The elevated abundance of a number of other trace metals, e.g. Pb, Zn, Cd, Cu, As and La, was detected in samples with an enhanced content of sulfur or phosphorus. The remarkably different behavior of the listed elements in two examined GA sequences could suggest that somewhat different sets of metal sequestration driving processes were responsible for the development of trace elemental assemblages in E and NW Estonian settings. As the trace element composition of GA is dominated by common marine redox sensitive and/or stable sulfide forming metals, the syngenetic trapping of metals from sea and interstitial water in redox boundary zones probably had first rate control over the development of trace element enrichment patterns. However, the observed high variability in the trace metal composition of GA, including heterogeneous REE patterns, points to the polygenetic nature of metal assemblages, apparently formed as the cumulative product of multistage evolution. On the whole, the study demonstrates that the knowledge base about metal distribution in GA is still rather fragmentary and that detailed geochemical, as well as multidisciplinary investigations are essential for adequately predicting potential metal resources of GA in the future.

doi: 10.3176/oil.2013.3.02

Acknowledgements

The authors are thankful to the reviewers for their constructive criticism and for helping to improve the manuscript. This study was funded by the Estonian Science Foundation Grant No. 8963 and the Estonian Ministry of Education and Research target research project No. SF0140016s09.

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Presented by J. Boak

Received October 30, 2012

MARGUS VOOLMA *, ALVAR SOESOO, SIGRID HADE, RUTT HINTS, TOIVO KALLASTE

Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia

* Corresponding author: e-mail voolma@gi.ee

Table 1. Major elements in GA samples from Pakri and Saka sections

Interval, cm                         GI XRF %
From    To   Sample    Si[O.sub.2]   Ti[O.sub.2]   [Al.sub.2]
                                                   [O.sub.3]

0       20   Pakri1    46.10         0.72          13.91
20      40   Pakri2    45.74         0.71          13.60
40      60   Pakri3    46.83         0.70          13.55
60      80   Pakri4    48.77         0.72          13.66
80     100   Pakri5    48.01         0.72          13.60
100    120   Pakri6    47.57         0.72          13.38
120    140   Pakri7    48.37         0.73          13.65
140    160   Pakri8    49.91         0.75          13.85
160    180   Pakri9    48.25         0.73          13.85
180    200   Pakri10   49.63         0.70          13.45
200    220   Pakri11   51.35         0.75          13.94
220    240   Pakri12   49.71         0.75          13.65
240    260   Pakri13   49.09         0.74          13.67
260    280   Pakri14   49.41         0.74          13.88
280    300   Pakri15   49.61         0.76          14.06
300    320   Pakri16   48.97         0.75          14.00
320    340   Pakri17   52.43         0.68          13.21
340    360   Pakri18   50.03         0.79          14.49
360    380   Pakri19   51.69         0.80          14.41
380    400   Pakri20   51.87         0.78          14.12
400    420   Pakri21   51.59         0.79          14.09
0       20   Saka1     49.73         0.73          11.94
20      40   Saka2     51.75         0.64          11.00
40      60   Saka3     48.28         0.64          11.27
60      80   Saka4     46.54         0.68          11.84
80     100   Saka5     49.95         0.70          11.55
100    120   Saka6     52.02         0.67          10.90
120    140   Saka7     48.01         0.65          11.01
140    160   Saka8     55.11         0.75          12.38
160    180   Saka9     48.86         0.64          10.91

Interval, cm                      GI XRF %
From    To   Sample    [Fe.sub.2][O.sub.3]   MnO     MgO

0       20   Pakri1    4.89                  0.020   1.31
20      40   Pakri2    4.01                  0.020   1.33
40      60   Pakri3    4.29                  0.019   1.30
60      80   Pakri4    4.33                  0.020   1.27
80     100   Pakri5    4.44                  0.020   1.26
100    120   Pakri6    4.07                  0.019   1.22
120    140   Pakri7    4.13                  0.018   1.22
140    160   Pakri8    4.36                  0.019   1.23
160    180   Pakri9    4.28                  0.018   1.23
180    200   Pakri10   4.95                  0.017   1.17
200    220   Pakri11   4.97                  0.017   1.18
220    240   Pakri12   4.25                  0.018   1.19
240    260   Pakri13   5.22                  0.019   1.25
260    280   Pakri14   6.08                  0.018   1.25
280    300   Pakri15   4.38                  0.019   1.30
300    320   Pakri16   4.44                  0.018   1.24
320    340   Pakri17   4.25                  0.019   1.16
340    360   Pakri18   4.21                  0.021   1.33
360    380   Pakri19   4.42                  0.021   1.33
380    400   Pakri20   4.72                  0.020   1.23
400    420   Pakri21   5.02                  0.022   1.27
0       20   Saka1     4.21                  0.009   0.72
20      40   Saka2     6.00                  0.008   0.64
40      60   Saka3     4.20                  0.009   0.67
60      80   Saka4     3.93                  0.012   0.87
80     100   Saka5     3.78                  0.012   0.87
100    120   Saka6     3.81                  0.011   0.78
120    140   Saka7     4.97                  0.012   0.82
140    160   Saka8     4.82                  0.018   0.98
160    180   Saka9     4.95                  0.033   0.82

Interval, cm                      GI XRF %
From   To    Sample    CaO    [Na.sub.2]O   [K.sub.2]O

0       20   Pakri1    0.25   0.07          8.00
20      40   Pakri2    0.22   0.07          7.77
40      60   Pakri3    0.20   0.07          7.73
60      80   Pakri4    0.23   0.06          7.95
80     100   Pakri5    0.13   0.06          7.82
100    120   Pakri6    0.12   0.06          7.85
120    140   Pakri7    0.11   0.07          7.92
140    160   Pakri8    0.10   0.07          8.02
160    180   Pakri9    0.12   0.06          8.12
180    200   Pakri10   0.16   0.06          7.88
200    220   Pakri11   0.15   0.07          8.25
220    240   Pakri12   0.13   0.07          8.12
240    260   Pakri13   0.14   0.07          7.77
260    280   Pakri14   0.21   0.07          7.72
280    300   Pakri15   0.18   0.07          8.20
300    320   Pakri16   0.10   0.07          8.15
320    340   Pakri17   0.60   0.07          7.91
340    360   Pakri18   0.18   0.07          8.44
360    380   Pakri19   0.23   0.07          8.42
380    400   Pakri20   0.18   0.07          8.32
400    420   Pakri21   0.43   0.08          8.16
0       20   Saka1     0.25   0.06          7.23
20      40   Saka2     1.08   0.06          6.59
40      60   Saka3     0.18   0.05          6.90
60      80   Saka4     0.11   0.06          7.17
80     100   Saka5     0.13   0.05          7.29
100    120   Saka6     0.13   0.05          6.90
120    140   Saka7     0.19   0.05          6.85
140    160   Saka8     0.25   0.06          7.51
160    180   Saka9     1.24   0.06          6.79

From   To    Sample    [P.sub.2][O.sup.5]    C1      S

0       20   Pakri1    0.15                 0.019   2.23
20      40   Pakri2    0.11                 0.020   1.96
40      60   Pakri3    0.12                 0.026   2.11
60      80   Pakri4    0.14                 0.022   2.16
80     100   Pakri5    0.12                 0.025   2.11
100    120   Pakri6    0.10                 0.023   2.02
120    140   Pakri7    0.12                 0.029   2.03
140    160   Pakri8    0.12                 0.023   2.12
160    180   Pakri9    0.09                 0.024   2.16
180    200   Pakri10   0.14                 0.018   2.56
200    220   Pakri11   0.18                 0.020   2.39
220    240   Pakri12   0.14                 0.023   2.08
240    260   Pakri13   0.13                 0.017   2.64
260    280   Pakri14   0.19                 0.017   2.98
280    300   Pakri15   0.13                 0.018   2.06
300    320   Pakri16   0.13                 0.019   2.18
320    340   Pakri17   0.48                 0.015   2.14
340    360   Pakri18   0.14                 0.017   1.95
360    380   Pakri19   0.17                 0.013   1.95
380    400   Pakri20   0.11                 0.014   2.23
400    420   Pakri21   0.27                 0.015   2.41
0       20   Saka1     0.37                 0.020   2.68
20      40   Saka2     1.08                 0.019   4.00
40      60   Saka3     0.54                 0.028   2.57
60      80   Saka4     0.25                 0.021   2.05
80     100   Saka5     0.29                 0.030   2.03
100    120   Saka6     0.24                 0.020   1.95
120    140   Saka7     0.20                 0.022   2.48
140    160   Saka8     0.23                 0.019   1.34
160    180   Saka9     1.33                 0.020   1.57

                       %             GI %
From    To   Sample    SUM     LOI500[degrees]C   LOI920[degrees]C

0       20   Pakri1    99.48       22.10            24.05
20      40   Pakri2    99.69       24.46            26.09
40      60   Pakri3    99.69       23.27            24.86
60      80   Pakri4    99.16       20.46            21.99
80     100   Pakri5    99.54       21.77            23.33
100    120   Pakri6    98.87       22.21            23.73
120    140   Pakri7    99.59       21.69            23.22
140    160   Pakri8    99.87       19.79            21.42
160    180   Pakri9    99.99       21.59            23.22
180    200   Pakri10   99.54       19.73            21.36
200    220   Pakri11   99.70       16.96            18.83
220    240   Pakri12   99.03       19.30            20.99
240    260   Pakri13   100.03      19.95            21.92
260    280   Pakri14   99.98       18.45            20.40
280    300   Pakri15   99.02       18.60            20.29
300    320   Pakri16   99.15       19.50            21.27
320    340   Pakri17   98.18       15.40            17.35
340    360   Pakri18   100.12      18.58            20.40
360    380   Pakri19   99.20       15.83            17.62
380    400   Pakri20   99.33       16.10            17.89
400    420   Pakri21   99.49       15.30            17.76
0       20   Saka1     99.99       21.28            24.73
20      40   Saka2     99.29       16.03            20.43
40      60   Saka3     99.05       23.70            26.29
60      80   Saka4     99.91       26.19            28.43
80     100   Saka5     99.84       22.83            25.19
100    120   Saka6     99.77       22.61            24.25
120    140   Saka7     99.80       24.96            27.02
140    160   Saka8     99.38       14.63            17.24
160    180   Saka9     99.29       19.71            23.63

Table 2. Trace elements in GA samples from Pakri and Saka sections

Interval, cm   Lab

From   To      Sample     Mo    Cu     Pb   Zn    Ni

0       20     Pakri1     639   146   105    45   130
20      40     Pakri2     181   115    75    40   124
40      60     Pakri3     203   134   101    49   166
60      80     Pakri4     148   133    98   845   178
80     100     Pakri5     155   143   116   138   170
100    120     Pakri6     151   133    98   134   144
120    140     Pakri7     157   148   105    42   147
140    160     Pakri8     126   151   193    39   141
160    180     Pakri9      88   162   143    39   115
180    200     Pakri10     74   152   135    38   160
200    220     Pakri11     61   151   135    60   107
220    240     Pakri12    102   129   132    50   115
240    260     Pakri13    110   161   152    40   172
260    280     Pakri14     60   162   174    37   185
280    300     Pakri15     92   131   103    40   133
300    320     Pakri16     85   144   117    42   120
320    340     Pakri17     96   120   105    38   113
340    360     Pakri18     53   141   103    41    96
360    380     Pakri19     57   129   100    42   104
380    400     Pakri20     52   125    94    40   116
400    420     Pakri21     65   101    88    36    99
0       20     Saka1     1143    76   193    14    829.
20      40     Saka2       85    85   187    10   1035.
40      60     Saka3       97   134   152    14    82
60      80     Saka4     1844   176   101    25    89
80     100     Saka5      202   122   135    22    89
100    120     Saka6      408   106   124    21    88
120    140     Saka7      413   108   137    36   127
140    160     Saka8      279   116   125   116   118
160    180     Saka9      299   148    95    23   125

Interval, cm   Lab

From   To      Sample     Co    As    U    Th

0       20     Pakri1     18    55   126   13
20      40     Pakri2     16    39   108   12
40      60     Pakri3     33    56   206   13
60      80     Pakri4     27    51    82   13
80     100     Pakri5     24    56   164   14
100    120     Pakri6     15    52   172   13
120    140     Pakri7     22    55   117   15
140    160     Pakri8     21    52    93   15
160    180     Pakri9     18    47    78   14
180    200     Pakri10    22    59    52   14
200    220     Pakri11    15    72    41   16
220    240     Pakri12    16    54    91   14
240    260     Pakri13    19    68    65   15
260    280     Pakri14    21   118    52   14
280    300     Pakri15    21    52    76   14
300    320     Pakri16    17    54   102   15
320    340     Pakri17    35    63    82   16
340    360     Pakri18    17    45    35   14
360    380     Pakri19    15    53    49   16
380    400     Pakri20    17    55    19   14
400    420     Pakri21    17    65    57   14
0       20     Saka1      44    64   137   13
20      40     Saka2     102    76   182   16
40      60     Saka3      62    86   169   15
60      80     Saka4      31    72   805   16
80     100     Saka5      43    54   111   16
100    120     Saka6      25    57   433   14
120    140     Saka7      28    50   239   14
140    160     Saka8      51    75   145   16
160    180     Saka9      53   236   184   15

Interval, ccmm           GI XRF   Acme    GI XRF   Acme
                                      PPM
From   To      Sample       Sr     Sb      V     Ba    Cr   Se

0       20     Pakri1       62     5.4    1081   398   45   3.7
20      40     Pakri2       65     4.3    1166   395   48   3.1
40      60     Pakri3       65     5.0    1223   381   51   3.5
60      80     Pakri4       63     3.9    1025   384   48   3.3
80     100     Pakri5       62     4.2    1061   369   50   3.7
100    120     Pakri6       64     4.4    1015   399   54   3.3
120    140     Pakri7       63     4.0    1229   347   57   4.1
140    160     Pakri8       64     3.3    1144   381   57   4.5
160    180     Pakri9       61     2.6     827   374   54   3.1
180    200     Pakri10      56     2.5     652   388   71   4.1
200    220     Pakri11      57     2.4     563   376   72   3.8
220    240     Pakri12      57     3.0    1040   387   65   4.7
240    260     Pakri13      55     4.4    1096   318   60   7.7
260    280     Pakri14      54     5.2     839   344   62   5.8
280    300     Pakri15      59     3.1    1081   408   57   4.3
300    320     Pakri16      56     3.5    1096   358   63   4.0
320    340     Pakri17      67     3.3    739    377   48   3.7
340    360     Pakri18      54     2.2    781    377   70   2.9
360    380     Pakri19      54     2.7    925    429   73   4.8
380    400     Pakri20      48     2.0    622    393   56   2.6
400    420     Pakri21      55     2.1    745    369   74   3.6
0       20     Saka1        62     9.1   1266    390   36   5.3
20      40     Saka2        56     5.3    946    409   36   5.7
40      60     Saka3        52     4.5   1093    406   32   5.3
60      80     Saka4        51     9.9   1497    438   41   5.5
80     100     Saka5        49     5.5   1453    435   38   5.1
100    120     Saka6        47     5.7   1288    441   30   4.3
120    140     Saka7        50     7.2   1165    390   31   4.1
140    160     Saka8        56     6.5   1096    421   38   5.6
160    180     Saka9        66     8.0    908    650   38   7.1

Interval, ccmm           GI XRF                       Acme
                                      PPM

From   To      Sample    Ga      Nb    Rb    Zr

0       20     Pakri1    17.8   13.6   128   129
20      40     Pakri2    15.6   13.5   127   128
40      60     Pakri3    15.7   13.0   127   133
60      80     Pakri4    14.2   12.5   121   134
80     100     Pakri5    15.0   17.2   125   132
100    120     Pakri6    15.2   19.5   124   138
120    140     Pakri7    14.9   15.2   125   136
140    160     Pakri8    14.0   14.0   126   142
160    180     Pakri9    15.6   14.3   124   131
180    200     Pakri10   14.6   11.9   113   137
200    220     Pakri11   14.5   12.8   117   144
220    240     Pakri12   12.9   12.6   125   144
240    260     Pakri13   16.8   13.9   115   139
260    280     Pakri14   12.5   10.7   105   140
280    300     Pakri15   15.0   14.0   128   140
300    320     Pakri16   16.2   15.9   128   138
320    340     Pakri17   13.9   10.6   118   148
340    360     Pakri18   16.7   13.2   131   142
360    380     Pakri19   16.5   12.7   128   150
380    400     Pakri20   15.9   12.3   121   153
400    420     Pakri21   13.7   13.4   119   157
0       20     Saka1     15.0   16.0   120   168
20      40     Saka2     12.0   10.0   92    171
40      60     Saka3     16.0   17.0   108   155
60      80     Saka4     16.0   19.0   141   165
80     100     Saka5     15.0   14.0   116   163
100    120     Saka6     13.0   16.0   122   160
120    140     Saka7     13.0   21.0   114   135
140    160     Saka8     11.0   16.0   121   173
160    180     Saka9     10.0   10.0   102   149

From    To     Sample    Y    Sc      Be     Li

0       20     Pakri1    23   3.3    1.8    17.3
20      40     Pakri2    19   3.5    1.6    18.0
40      60     Pakri3    19   4.5    2.3    18.8
60      80     Pakri4    27   4.5    2.1    16.4
80     100     Pakri5    18   5.0    2.3    18.7
100    120     Pakri6    17   3.8    2.0    15.3
120    140     Pakri7    20   4.8    2.0    17.1
140    160     Pakri8    18   4.6    1.3    16.3
160    180     Pakri9    13   4.4    1.4    15.3
180    200     Pakri10   24   4.2    1.6    14.5
200    220     Pakri11   17   4.2    1.3    14.6
220    240     Pakri12   21   n.a.   n.a.   n.a.
240    260     Pakri13   21   4.7    1.7    15.6
260    280     Pakri14   31   4.2    2.0    14.6
280    300     Pakri15   21   4.5    1.2    16.1
300    320     Pakri16   13   4.6    1.0    15.4
320    340     Pakri17   73   5.0    1.3    14.9
340    360     Pakri18   21   4.9    1.2    16.7
360    380     Pakri19   23   4.7    1.0    16.4
380    400     Pakri20   21   4.1    1.0    14.6
400    420     Pakri21   40   n.a.   n.a.   n.a.
0       20     Saka1      9   2.8    0.5    3.9
20      40     Saka2     31   3.6    0.6    3.1
40      60     Saka3     12   3.2    0.8    4.1
60      80     Saka4      6   4.8    1.2    9.1
80     100     Saka5     11   3.1    0.7    7.1
100    120     Saka6      9   3.0    0.7    6.9
120    140     Saka7     16   2.7    0.5    8.1
140    160     Saka8     23   3.8    0.9    9.8
160    180     Saka9     57   3.2    0.8    7.8

Table 3. Rare earth elements in GA samples from Pakri and Saka
sections, ppm

Lab    Sample    La      Ce      Pr     Nd     Sm     Eu      Gd

GI;    Pakri1    35.1    58.5    6.5   26.0    5.0   1.14    5.07
Acme
GI;    Pakri2    33.2    55.4    6.2   24.2    4.7   1.02    4.56
Acme
GI     Pakri3    33.6    57.7    6.6   26.1    5.3   1.12    4.92
GI     Pakri4    37.5    68.6    8.1   32.5    6.6   1.38    6.28
GI     Pakri5    35.9    62.4    7.2   28.1    5.6   1.16    5.11
GI;    Pakri6    35.9    61.0    6.9   26.5    5.1   1.07    4.70
Acme
GI     Pakri7    37.5    65.8    7.6   29.6    5.8   1.17    5.09
GI     Pakri8    39.6    68.1    7.6   29.2    5.5   1.09    4.80
GI     Pakri9    35.1    58.5    6.4   23.8    4.3   0.88    3.81
GI     Pakri10   39.2    76.0    9.1   36.4    7.2   1.43    6.30
GI     Pakri11   39.2    72.4    8.3   31.5    5.9   1.14    4.98
GI;    Pakri12   38.1    70.0    8.2   31.9    6.2   1.23    5.41
Acme
GI     Pakri13   39.7    71.8    8.3   32.3    6.2   1.25    5.45
GI     Pakri14   43.8    85.4   10.3   41.7    8.4   1.69    7.57
GI     Pakri15   39.2    72.0    8.4   33.2    6.6   1.36    5.91
GI     Pakri16   34.8    58.0    6.4   24.1    4.5   0.93    3.99
GI     Pakri17   56.0   138.2   18.4   81.6   17.7   3.51   16.23
GI     Pakri18   37.6    69.3    8.1   32.6    6.5   1.35    5.83
GI     Pakri19   38.4    71.6    8.4   33.9    6.8   1.42    6.13
GI     Pakri20   34.6    63.9    7.4   29.5    5.9   1.23    5.25
GI;    Pakri21   40.4    82.3    9.9   41.5    8.6   1.86    8.01
Acme
Acme   Saka1     26.9    37.7    3.6   11.2    2.0   0.41    1.34
Acme   Saka2     36.5   119.0   16.4   68.6   15.3   2.93   11.00
Acme   Saka3     20.0    41.7    5.9   26.8    6.2   1.23    4.81
Acme   Saka4     19.5    27.6    2.7    9.0    1.5   0.32    1.03
Acme   Saka5     21.3    33.7    3.5   12.1    2.2   0.41    1.66
Acme   Saka6     18.6    29.6    3.0   10.0    1.9   0.39    1.38
Acme   Saka7     23.4    43.4    4.8   18.3    3.5   0.69    2.74
Acme   Saka8     30.9    61.1    7.4   27.0    5.7   1.11    4.47
Acme   Saka9     42.6    97.0   12.8   52.2   11.2   2.27   10.17

Lab    Sample     Tb      Dy     Ho     Er    Tm      Yb     Lu
GI;    Pakri1    0.70    4.22   0.83   2.51   0.37   2.46   0.35
Acme
GI;    Pakri2    0.63    4.03   0.79   2.53   0.37   2.67   0.38
Acme
GI     Pakri3    0.70    4.43   0.85   2.63   0.37   2.56   0.35
GI     Pakri4    0.90    5.81   1.12   3.54   0.50   3.48   0.49
GI     Pakri5    0.72    4.62   0.89   2.85   0.42   2.90   0.41
GI;    Pakri6    0.66    4.25   0.82   2.66   0.40   2.81   0.40
Acme
GI     Pakri7    0.72    4.54   0.88   2.83   0.42   3.05   0.43
GI     Pakri8    0.67    4.36   0.87   2.90   0.44   3.24   0.46
GI     Pakri9    0.52    3.42   0.70   2.38   0.37   2.79   0.41
GI     Pakri10   0.90    5.67   1.10   3.51   0.52   3.63   0.52
GI     Pakri11   0.70    4.49   0.89   2.99   0.46   3.40   0.50
GI;    Pakri12   0.77    4.93   0.96   3.15   0.47   3.37   0.49
Acme
GI     Pakri13   0.78    5.00   0.98   3.21  0.49    3.48   0.50
GI     Pakri14   1.11    6.93   1.34   4.22  0.60    4.12   0.59
GI     Pakri15   0.84    5.28   1.01   3.23  0.48    3.40   0.48
GI     Pakri16   0.55    3.57   0.71   2.39  0.37    2.76   0.40
GI     Pakri17   2.38   14.48   2.71   7.86  0.99    6.04   0.82
GI     Pakri18   0.83    5.26   1.03   3.33  0.50    3.55   0.52
GI     Pakri19   0.87    5.44   1.05   3.36  0.49    3.51   0.51
GI     Pakri20   0.75    4.78   0.94   3.07  0.46    3.34   0.49
GI;    Pakri21   1.17    7.23   1.39   4.29  0.59    4.01   0.56
Acme
Acme   Saka1     0.26    1.45   0.32    0.97  0.18   1.24   0.19
Acme   Saka2     1.70    8.19   1.35    3.39  0.51   3.30   0.45
Acme   Saka3     0.74    3.37   0.57    1.62  0.23   1.58   0.22
Acme   Saka4     0.19    1.12   0.24    0.68  0.14   0.98   0.14
Acme   Saka5     0.28    1.78   0.41    1.36  0.25   1.95   0.29
Acme   Saka6     0.25    1.53   0.34    1.14  0.20   1.73   0.24
Acme   Saka7     0.48    2.75   0.56    1.61  0.31   2.03   0.27
Acme   Saka8     0.78    4.29   0.88    2.74  0.43   3.09   0.45
Acme   Saka9     1.68    9.21   1.83    5.20  0.76   5.03   0.65
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Author:Voolma, Margus; Soesoo, Alvar; Hade, Sigrid; Hints, Rutt; Kallaste, Toivo
Publication:Oil Shale
Article Type:Report
Geographic Code:4EXES
Date:Sep 1, 2013
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