Till Stratigraphy and Geochemical Differences Between Till Beds in Western Finland

Complexity of glacial dispersal and hydromorphic processes in till geochemistry Edited by Marja Liisa Räisänen and Maria Nikkarinen Geological Survey of Finland, Special Paper 34, 21– 42 , 2003.

T ILL S T RAT IGRAPHY AN D GE O C HE MIC AL DIFFE RE N C E S BETWEEN TILL BEDS IN WESTERN FINLAND

by Esko Iisalo

Iisalo, Esko 2003. Till stratigraphy and geochemical differences between till beds in western Finland. Geological Survey of Finland, Special Paper 34, 21–42, 6 figures and 7 tables. The element concentrations and particle-size distributions in samples taken from till beds of various ages in Ostrobothnia (Pohjanmaa), western Finland, are examined. The fine fraction <0.074 mm of the samples was separated by sieving. The fine fractions of the till samples were leached in hot aqua regia at 90oC, and elements in solution were determined using the ICP-AES technique. Particle-size distributions were determined by sieving and clay concentrations of the fines by sedigraph. Generally, the element concentrations in the various tills differ only slightly. However, statistically detectable differences were found in the concentrations of Al, Fe, Ca and S. High concentrations of Al and S were found in the uppermost Weichselian till, which is sand-dominated and poor in fines. The lower Weichselian till differed from the other till units by its high concentration of fines, K and S. This was considered to be due to mixing of S-bearing Eem sediments with the younger till. The lowermost Saale till was highest in Ca. The clay contents of the till units correlate with the element concentrations. High clay concentrations cause increases in background concentrations in element maps based on till fines. However, these changes in concentrations are small compared with those caused by rock types in the bedrock. The differences in particle-size distributions and element concentrations between the lower and upper Weichselian till were considered to be partly due to deglaciation, which occurred in supra-aquatic conditions, and the subsequent interstadial, the exact time of which around the Mid-Weichselian has not been possible to determine.

Key words (GeoRef Thesaurus, AGI): till, stratigraphy, grain size, geochemistry, trace elements, Quaternary, Pleistocene, Weichselian, Eemian, Saalian, North Ostrobothnia, Central Ostrobothnia, Finland

Esko Iisalo Geological Survey of Finland, P.O.1237, FIN-70211 KUOPIO, FINLAND

E-mail:[email protected]

21 Geological Survey of Finland, Special Paper 34 Esko Iisalo

INTRODUCTION

The study area is located in western Finland, central 0.06 mm, consists of silt and clay. The concentration Ostrobothnia between the municipalities of Kaus- of clay clearly correlates with element concentrations tinen and Rantsila (Fig. 1). The particle-size distribu- and specific surface measured in the fines (Nieminen tions and element concentrations in till beds of various 1985, Lintinen 1989). Heavy metal concentrations of ages and in interglacial sediments found between clays in southwestern Finland are two or three times them are examined using material collected from test higher than those of till fines in the same area (Salminen pits. The correlation of observations from various et al. 1997). The clays contain more of the major parts of the study area is facilitated by representative elements Al, Fe, K and Mg, and less of the elements stratigraphic sequences found in the area, dating Si, Na and Ca than do the tills. However more than from the Saalian-Eemian-Weichselian periods. The twice the clay concentrations (above background) results are applied to the identification of till beds of have been found in a multiple element anomaly in till various ages, interpretation of geochemical till maps fines which extends from central Ostrobothnia to and studies of transport of ore boulders. When Savo and is visible onregional geochemical maps geochemical maps based on till samples are used for (Lintinen 1995, Räisänen et al. 1992, Salminen 1995). prospecting, it is necessary to distinguish between Within this anomaly it is possible to distinguish anomalies caused by the rock types and other types heavy metal anomalies caused by the bedrock, of anomaly, caused by differences in particle-size including the copper anomaly of the Ylivieska basic distribution or stratigraphic variations in the till metavolcanite and the nickel anomaly of the Alavieska beds, by admixture of old sediments into the till, and peridotite. Anomalous till has been transported over by regional variations in glacial dynamics. 5 km southeastwards from its source by the last The fine fraction of the till, with grain size less than glacial flow (Iisalo & Junnila 1984, Iisalo 1992).

Fig. 1. The study area showing waterways, sites referred to in the text and the test pits.

22 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds...

In a study of the Ruukki area the concentrations are low. It has been shown both experimentally and of fines in till were found to be inversely proportional by calculation that the fines of the Weichselian till in to the specific gravity. This is due to washing of the the Ylivieska area contain mainly (87 %) till, by which the light clay minerals are removed, the resedimented older till and sediment material. The average specific gravity of the remainder increases study is based on effects of grinding and chemical (Mäkinen 1992). These minerals are mainly quartz factors on the composition of the till fine fraction and feldspars, in which trace metal concentrations (Mäkinen 1995, Mäkinen, this issue).

EFFECTS OF BEDROCK UPON TILL GEOCHEMISTRY AND LITHOLOGY

The bedrock of the area consists of Svecofennian Iisalo 1994, 1995). schists, which are mainly mica gneiss and mica Lithological counts were made at a depth of 1.5- schist, partly various metavolcanic rocks and black 3.5 m in test pits. The results are included in the schists. The most common plutonic rocks are gran- preliminary reports (1973-1981) of the geochemical ite and granodiorite, while diorite and gabbro play a mapping performed by the Geochemical Department lesser role. of the GSF (Geological Survey of Finland). The tills Basic metavolcanic rocks are distinguished on the of the study area consist of about 80 % of granitoid geochemical till maps by copper and sulphur anoma- rocks, mica gneisses and mica schists. The propor- lies, mica gneisses as multimetal anomalies and tions vary regionally according to the dominating black schists as zinc-nickel anomalies. The basic rock types. Basic plutonic rocks, metavolcanites plutonic rocks are reflected by nickel-chrome anoma- and other minor rock types make up about 20 %. In lies, whereas in areas with granitoid rocks the metal the till beds of the Vihanti area the dominating rock concentrations are low (Iisalo & Junnila 1984, types are also granite and gneiss (Hyyppä 1948).

GLACIATIONS, EEMIAN INTERGLACIAL AND INTERSTADIALS

In Ostrobothnia numerous observations have been glacial period, during which the fine-grained sedi- made of sediments formed in the Eemian Baltic Sea, ments were mixed with till, which is often dominated which separate the lower Saalian till beds from by silt and sand. The till contains interglacial pollens those of the upper Weichselian. The oldest known and has a high sulphur content (Heinonen 1957, till in the area was formed during the Saalian glacial Iisalo 1992). The till has been transported east- period, when the ice sheet was at its largest, extend- southeastwards (Nenonen 1992, Iisalo 1992). The ing to Continental Europe and southern Russia Odderade interstadial, which is younger than the (Donner 1995). This is a sandy till, which in central Brörup is known in northwestern Europe. Ostrobothnia has been transported from northwest Evidence of two Weichselian till beds of different toward southeast (Nenonen 1992). During the age was obtained from central Ostrobothnia, where melting of the Saalian ice sheet, eskers were formed esker formations were found between till beds in Ostrobothnia, including the till-covered eskers of transported from different directions (Iisalo 1992). Norinkylä in Teuva (Niemelä & Tynni 1979) and Radiocarbon and OSL (optically stimulated lumi- Oulainen (Forsström 1982). nescence) datings of the sand and organic deposits The warm Eemian interglacial was characterized in the surficial part of the esker at Mertuanoja in by the spreading of demanding deciduous trees to Ylivieska (Iisalo 1992, Nenonen 1995) indicate an northern latitudes. The Eemian Baltic Sea, which interstadial dating in the period 36 000 - 72 000 BP was more extensive than the present Baltic, was in (dating methods are not exact). The samples con- connection with the Arctic Ocean (Grönlund 1991). tain pollen of mainly dwarf shrubs and birch, which In Ostrobothnia the sea level extended 120 m higher indicates a cold subarctic climate. It has been than at present, and fine-grained sediments were suggested that the silty till, transported from the deposited. The interglacial was followed by the cool west and older than the esker, was formed during a Brörup interstadial and then by the Weichselian glaciation that occurred from Early Weichselian to

23 Geological Survey of Finland, Special Paper 34 Esko Iisalo the early part of the Middle Weichselian (from the Reisjärvi, Sievi and Pyhäjoki areas have been trans- Brörup interstadial to the Odderade interstadial) ported in the same direction (Salonen 1986). How- (Iisalo 1996). ever, the combined effect of the glaciations must be No interstadial deposits had previously been found taken into account regarding the transport of boul- between the Weichselian tills south of Oulu. For this ders and geochemical anomalies. The geometric reason it had been proposed that there was only one mean transport distance of surficial boulders in till is Weichselian glaciation in central and southern Fin- over 5 km north of Kalajoki and 0.5-5 km south of land (Hirvas & Nenonen 1987, Sutinen 1992, Kalajoki. The Weichselian ice sheet was at its Nenonen 1995). greatest extent during the Late Weichselian about The silty till and interstadial eskers are overlain by 20 000 years ago, when the margin extended to a younger Weichselian sandy till, which in central Northern Germany (Donner 1995). After melting of Ostrobothnia has been transported southeastward the ice sheet and the following ice lake and sea parallel to the drumlins, (Okko 1949, Kauranne stages, weathering and podzolization processes 1979, Iisalo 1992). Several of the geochemical started affecting particle-size distribution and ele- multielement anomalies crossing central Ostro- ment concentrations in surface layers of the till. bothnia are oriented in this direction of transport Podzolization involves enrichment of iron and alu- (Salminen 1995). The surficial till boulders in the minium in the surface layers of soil (Räisänen 1995).

MATERIAL AND METHODS

Study area and sampling sites

Differences in particle-size distribution and ele- ined in till samples from the area, some of them mentcomposition between till beds were exam- taken earlier (Iisalo 1992), some new. All samples

Table 1. Particle sizes in different till beds and sediments.

LAYER D50_MM FINES CLAY_FIN CLAY_TOT

EMean 93.160 25.720 24.080 Median 90.000 25.500 25.500 Maximum 100.0 35.7 32.1 Minimum 86.2 10.1 8.7 Std. 6.2971 10.5053 9.6116 Deviation N 555

SMean.111 38.092 17.725 6.675 Median .110 40.000 18.200 6.950 Maximum .2 45.3 26.6 8.8 Minimum .128.9 8.4 2.6 Std. .0298 5.9644 5.8006 2.0477 Deviation N 912 12 12

W I Mean .120 42.826 14.833 6.423 Median .110 42.000 14.800 5.645 Maximum .5 80.0 29.0 13.5 Minimum .0 29.9 3.5 1.1 Std. .1056 12.9328 7.2718 4.0808 Deviation N 23 23 27 24

W II Mean .20131.827 16.069 5.466 Median .140 29.700 14.900 4.245 Maximum .9 53.0 33.0 15.5 Minimum .115.0 4.2 1.2 Std. .1646 9.0765 7.4051 3.9217 Deviation N 29 30 35 30

24 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... 511P S_511P 895.51338.15 872.00 50.00 922.18 80.89 377.86 922.36 136.14 297.50 907.00 50.00 79.41 352.93 861.21 271.95 58.00 328.50 854.50 88.45 58.00 400.00 969.50 97.00 511P MG_511P MN_511P NA_511P P_ 511P K_ 511P FE_ 6 666 6 6 6 6 6 98 98 98 98 98 98 98 98 98 1414141414 1414 14 14 50 50 50 50 50 50 50 50 50 28 28 28 28 28 28 28 28 28 4060 1690 7380 448 1830 85 184 421 4 5840 2500 7380 448 1830 85 184 421 36 4540 1690 10400 564 1880 88 186 446 6 4060 2000 9600 558 1930 85 192 710 4 2380010400 5100 3600 37100 18700 5100 1900 13300 4900 654 204 800 300 1240 524 8090 161 17400 5040 26500 5440 8900 360 589 1080 2340 23900 5280 37700 6460 13300 654 800 1480 8090 12500 4930 21900 2300 6940 245 600 1220 503 23900 5280 37700 6460 11800 421 533 1480 515 7300.00 4200.00 15050.00 2050.00 4600.00 1 9612.14 3904.64 17350.00 2321.82 4821.43 1 9565.00 3825.00 17650.00 1945.00 4590.00 173.50 315.00 8265.71 4125.00 15284.29 1794.29 4466.43 176.37 9095.00 3925.00 15350.00 2060.00 4365.00 1 16516.6717100.00 4250.00 28466.67 4050.00 29300.00 3850.00 4050.00 9266.67 9650.00 371.33 265.00 516.67 500.00 770.67 715.50 3262.33 1484.50 5693.651 665.582 8861.076 1367.845 3828.664 215.640 183.485 248.835 3659.954 4614.336 706.529 6772.198 1254.698 2540.355 97.256 111.656 173.867 1151.172 10692.96 3852.24 18712.04 2154.10 5156.94 195.39 340.05 2125.008 606.868 3563.846 587.668 1143.898 51.089 112.579 186.973 132.683 11279.00 3698.80 19264.00 1957.42 5045.00 188.54 301.06 10040.00 3675.00 17800.00 1560.00 4325.00 166.00 4763.828 691.005 6871.733 1266.301 2576.582 81.195 78.706 192.133 108.477 3832.982 739.772 5356.097 1194.061 1910.820 68.779 102.713 83.284 449.442 Median Maximum Minimum Std. Deviation N Median Deviation N Median Maximum Minimum Std. Deviation N Maximum Minimum Std. Median Median Deviation N Maximum Minimum Std. Deviation N Maximum Minimum Std. EMean W I Mean Total Mean SMean W II Mean LAYER AL_511P CA_ Table 2. Major element distribution in different till beds and sediments.

25 Geological Survey of Finland, Special Paper 34 Esko Iisalo were taken in test pits dug by excavator where during 1993-1996 in the districts of Oulainen and clearly distinguishable till beds, differing in appear- Ylivieska. In these pits samples were taken not only ance and properties occurred. The distinction of till of the till which served as sedimentation base for the beds was based on boundaries between beds, till eskers but also of the till covering the eskers. Samples fabric analyses, and differences in particle-size distri- of till beds formed during three different glacial bution and colour. stages were taken at Mertuanoja in Ylivieska (Iisalo Samples were taken from three different till beds. 1996), where esker deposits and Eemian sediments The uppermost bed in the stratigraphic sequence is separate the till beds. Samples of Saalian till (S till) here called the WII till, which was defined in earlier which served as the sedimentation base for intergla- studies (Okko 1949, Kauranne 1979, Iisalo 1992) cial sediments and eskers were obtained at as having formed during the younger stage of the Mertuanoja, Vuojalankangas in Oulainen and Weichselian glacial period. The older Weichselian Vesiperä in Haapavesi (Nenonen 1995). Two stage is represented by the WI till, which at Mertuanoja samples interpreted as Saale till come from in Ylivieska and Porkankangas in Kärsämäki is the Näsälänperä in Pulk-kila. They were taken from a sedimentation base for esker formations covered by depth of 4 m, below two till beds and a sand deposit. the WII till. This is sand-dominated with a southeast- Grain size analyses were made on 23 WI, 37 WII trending fabric. The WI till, which was transported and 12 S till samples respectively (Table 1). Chemi- from the west or west-northwest, is bluish gray and cal analyses were made on 28, 50 and 15 samples of contains abundant fines. Samples of the WI and WII the above categories (Tables 2 and 5). tills are from 34 test pits, which were dug in central Since admixture of interglacial and interstadial sedi- Ostrobothnia in the map sheet areas of Kaustinen ments has affected the properties of Weichselian tills, 2323, Ylivieska 2431, Piippola 3411 ja Rantsila this study also included fine-grained Eemian sedi- 3412 during 1973-1981 and in the map sheet areas ments from the Mertuanoja and Vesiperä sites. Grain- of Vihanti 2434 and Ruukki 2443 in 1996 (Fig.1). size analyses were performed on 5 samples and In addition test pits were dug in till-covered eskers chemical analyses on 6 samples (Tables 2 and 5).

Sample preparation and analysis

Samples were dried at a temperature of 70o C, than fresh minerals (Nieminen 1985). As the acid and the fine fraction was separated by sieving. The mixture totally dissolves the mica and clay minerals fine fractions were leached in hot aqua regia at 900o which are also the bearers of sulphides and metals, C, and elements in solution were determined using the aqua regia leach is widely used in ore exploration the ICP-AES technique. The analyses were done at and geochemical mapping. the Chemical Laboratory of the GTK in Kuopio. Particle-size distributions were determined by siev- When using the aqua regia leach it must be taken ing and clay concentrations of the fines by sedigraph. into consideration that major silicate minerals such In this study the following quantities were examined: as quarz, K feldspar and Na-dominated plagioclase the D50 value, which reflects the mean particle-size are not totally dissolved, whereas micas, sulphides, distribution of the till beds, the amount of fines clay minerals and precipitates are completely dis- (<0.06 mm) in the till, the amount of clay (<0.002 solved (Räisänen et al. 1992). Weathered minerals, mm) in the fines, and the amount of clay in the total which have a large specific surface, are more soluble till sample.

RESULTS

Particle-size distribution in till and interglacial sediments

Till bed S the stratigraphic sequence of the study area, occurs on a depth of 4-8 m (Table 1, Fig. 2). At most of the The S till, which is the lowermost known till bed in studied sites it is covered by sediment ascribed to the

26 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds...

Eemian interglacial. The S till contains around 38% clay (6.4 %) in the total till material is greater than in fines, less than the overlying WI till.The S till fines the WII till (5.5 %). The average particle size of the contain somewhat more clay (18%) than other tills, till is markedly finer than that of the upper WII till, but the differences are not statistically significant. which is reflected by a fairly low D50 value (0.12 According to the Finnish technical classification (RT mm). The till is a silty sand till. classification) the S till is a sandy silt till, with a D50 value of 0.11 mm. Till bed WII The exceptionally high concentration of fines (45%) in the few samples from the Mertuanoja bog basin Compared with the lower WI till the WII till is raise the mean concentration of fines. At Vesiperä in coarser-grained and contains clearly less (32%) fines. Haapajärvi, the concentration of fines in the S till is However, the concentration of clay in the fines is only 28%. According to earlier studies (Nenonen slightly higher in WII than in WI, which contains 1995) and visual observations in the course of this abundant silt. These are sandy tills and silty sand tills study at Vuojalankangas in Oulainen, the S till is with an average D50 value of 0.20 mm. generally a sandy till, fairly poor in fines. The average clay contents of the fines of various tills are of the same order of magnitude. Till bed WI Eemian sediments On the study sites the boundary surface between till beds WI and WII is on a depth of 1.5-6.0 m. The Two of the five studied samples of Eemian sedi- WI till is characterized by a high concentration of ment consist of fines, silt and clay. In addition to the fines (43 %). A significantly great part of the fines is fines, three of the samples contain a fine sand silt. Due to the high silt concentration the concentra- fraction. On average the samples contain 6% sand, tion of clay fraction in the fines (15 %) is no higher 68% silt and 26% clay. The average clay concentra- than that of other tills, although the concentration of tion of the fines is nearly twice that of the tills.

ELEMENT DISTRIBUTION

Major elements

The averages, medians, maxima, minima and stan- minium, iron and manganese in the till beds are dard deviations of the major element analyses of highest in the uppermost WII till and lowest in the various till bed fines are shown in Table 2 and lowermost S till (Table 2, Fig. 3a). The difference in Figures 3 a, b. This statistical analysis showed the concentrations is significant between the upper WII following groups of elements to have (Table 4) the till and the lower WI till, whereas the difference highest correlations, which stand out in the form of between the WI till and the S till is smaller. factors in Table 3: 1. aluminium, iron and manga- Aluminium and iron concentrations of the Eemian nese, 2. calcium, sodium and phosphorus, 3. mag- sediments are clearly higher than those of the tills, nesium and potassium and 4. sulphur. and manganese concentrations are more than double The element distributions in Eemian sediments that those of the tills. contain abundant clay differ clearly from those of the tills. The concentration levels in the sediment fines Calcium, sodium and phosphorus aregenerally higher than those of the tills (Table 2). According to factor analysis the elements have a Aluminium, iron and manganese significant loading in factor 2. Phosporus has the highest loading in factor 3. Average concentrations in According to factor analysis in Table 4 these ele- the till beds increase downwards (Table 2, Fig. 3a). ments have a significant loading in factor 1 (Table 3). There is a marked change in calcium between the Iron correlates well with manganese (0.87) and alu- uppermost WII till and the lowermost S till. The minium (0.75). The average concentrations of alu- differences in concentration of sodium and phospho-

27 Geological Survey of Finland, Special Paper 34 Esko Iisalo ne inside the Fig. 2. Results of particle-size analysis of the till box beds. The identifies box contains the the middle group 50 percent median. of values Fines=till in a fines, group. The clay_fin=clay li in fines, clay_tot=total clay in till sample.

28 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... Fig. 3a. Concentrations of Al, Fe, Mn, Ca, Na and P in different till beds.

29 Geological Survey of Finland, Special Paper 34 Esko Iisalo Fig. 3b. Concentrations of Mg, K and S in different till beds and sediments.

30 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds...

Table 3. Factor analysis of the element distributions.

Component

123456

CU_511P .941

NI_511P .860 .354

ZN_511P .820 .542

CO_511P .715 .578 .328

K_511P .701.554 -.300

FE_511P .681.604 .218

MN_511P .656 .432 .465

AL_511P .391.856 .213

BA_511P .343 .851.224

V_511P .510 .758 .314

MG_511P .616 .719

CR_511P .573 .686 .353

TI_511P .312 .662 .573

SR_511P .348 .868

NA_511P .862 -.374

CA_511P .827 .525

P_511P .976

S_511P .990

Extraction Method: Principal Component Analysis. Rotation Method: Varimax with Kaiser Normalization.

Rotation converged in 8 iterations. rus between the different till beds are minor. The greatest potassium concentration is found in the WI highest concentrations are found in the lowermost S till, which also has the greatest amount of silt and fines. till. The average concentrations of sodium in the WI The potassium concentration in the lowermost S till is till and the S till are almost equal despite the great clearly smaller than in the WI till. deviation. The median concentration of sodium is The concentrations of magnesium and potassium in greatest in the S till. the Eemian sediments are nearly double those of the tills. The clay-rich Eemian sediments clearly contain more sodium than the tills. Compared with other Sulphur elements the concentrations of calcium and phosphorus in the sediments are exceptionally low. Cal- The highest sulphur concentrations are found in the cium concentrations of the sediments are only slightly WI till overlying the Eemian sediments (Table 2, Fig. higher than those of the tills. Phosphorus concentra- 3b). The average concentration is raised by the tions of the sediments are lower than those of the tills. exceptionally high maximum of 2340 ppm, close to that found in sulphide clays. A dark gray colour and Magnesium and potassium strong sulphurous odor are characteristic of tills containing abundant sulphur. The sulphur concentrations Magnesium concentrations of the till beds are and their deviations in the uppermost WII till are greatest in the WII till and smallest in the lowermost clearly lower than those of the WI till. The average S till (Table 2, Fig. 3b). Due to the great deviation the sulphur concentration in the lowermost S till is clearly differences in concentration are not significant. The lower than in the WI till, but slightly higher than in the

31 Geological Survey of Finland, Special Paper 34 Esko Iisalo

Table 4a. Major element correlation coefficients.

AL_511P CA_511P FE_511P K_511P MG_511P MN_511P NA_511P

CA_511P Pearson .162 Correlation N 98 FE_511P Pearson .797 .319 Correlation N 98 98 K_511P Pearson .577 .210 .726 Correlation N 98 98 98 MG_511P Pearson .822 .389 .812 .807 Correlation N 98 98 98 98 MN_511P Pearson .590 .500 .824 .708 .737 Correlation N 98 98 98 98 98 NA_511P Pearson .207 .520 .394 .437 .372 .584 Correlation N 98 98 98 98 98 98 P_511P Pearson .108 .501 .150 .001 .238 .097 -.199 Correlation N 98 98 98 98 98 98 98

Table 4b. Trace element correlation coefficients.

BA_511P CO_511P CR_511P CU_511P NI_511P PB_511P SR_511P TI_511P V_511P

CO_511P .823 N 55 CR_511P .861.856 N 50 93 CU_511P .525 .748 .650 N 55 98 93 NI_511P .620 .864 .790 .765 N 50 93 93 93 PB_511P .503 .501.383 .700 .426 N 50 93 93 93 93 SR_511P .515 .539 .579 .220 .333 .053 N 50 93 92 93 92 92 TI_511P .769 .737 .772 .386 .607 .292 .776 N 5194 93 94 93 93 93 V_511P .900 .852 .908 .571.787 .306 .589 .805 N 5194 93 94 93 93 93 94 ZN_511P .788 .918 .807 .821 .904 .616 .377 .668 .827 N 55 98 93 98 93 93 93 94 94

WII till. Although the differences of average concen- regional distribution of sulphur. trations between the till beds are distinct, their signifi- The sulphur concentrations (maximum 8090 ppm) cance level according to the T test is not very high in the Eemian sediments are several times those of till. due to the strong deviation, which reflects the uneven

TRACE ELEMENTS

In the till beds and Eemian sediments the average, ment calcium. Most of the correlation coefficients median, standard deviation, maximum and minimum between the trace elements reflect a strong (>0.5) of the concentration was calculated for the following linear dependence (Table 4). elements: barium, cobalt, chromium, copper, titanium The differences between average concentrations in (minor element), vanadium, strontium and zinc, and the till beds are small. The concentrations in the shown in Table 5. According to factor analysis these lowermost S till seem to be lower than in the other till elements have high loadings in factor 1 (Table 3). An beds, but the differences are not significant. Only the exception is strontium, which follows the major ele- concentration of zinc in till bed S is significantly smaller

32 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... 511P 511P ZN_ 511P V_ 511P SR_511P TI_ 511P PB_ 511P CU_511P NI_ 511P CR_ 6656555 556 9141214121212 131314 2920 2.728 28 1520 2.8 27 528 50 16 2855 2.7 7 49 27 5 98 15 3 50 27 6 93 49 5 6 27 2 98 49 6 859 27 93 8 49 22 2 27 93 947 49 15 6 28 93 25 49 859 94 13 50 22 94 13 98 70 7.46846 33 9.8 2.8 13 46 15 15 36 6 5 26 6 14 8 3 1410 22 11 44 1850 29 986 59 24 40 15 115 12.2133 44 15.7 74222 62 41 21.1 79 27 70 58 20 79 18 2060 58 25 59 27 2170 71 25 77 2310 94 85 94 222 21.1 70 64 43 25 21 2310 85 89 59.3963.00 6.838 6.8507.524 28.3563.59 1.8624 27.8056.95 17.29 7.261 7.750 12.35 6.875 14.54 10.651 28.90 14.0066.62 27.1061.25 3.82 5.543 18.96 4.00 7.196 14.35 6.670 1.661 14.55 16.47 13.25 29.32 14.8070.04 27.1063.00 3.081 1424.31 6.01 1380.00 19.01 4.32 7.566 14.85 6.890 37.12 244.099 34.50 14.35 15.82 13.80 30.10 14.30 9.199 28.50 28.80 29.50 1492.19 4.68 1460.00 19.63 2.50 5.895 14.50 40.47 39.20 14.22 16.36 13.50 14.70 35.61 32.45 1442.39 5.28 1460.00 4.00 41.94 39.30 14.45 13.70 34.57 31.55 1476.51 1455.00 41.88 39.25 35.81 30.70 26.712 2.7946 9.08429.229 13.767 3.3127 7.438 9.66033.921 4.885 14.847 3.5630 3.556 8.439 10.530 336.014 3.254 14.889 12.211 3.431 8.188 14.695 250.993 4.204 11.815 3.395 17.201 298.286 12.701 17.350 118.95110.00 13.767 12.30055.588 48.42 38.00 6.1675 33.33 16.819 21.15 25.46 23.983 22.10 10.78 11.238 8.00 8.031 17.04 16.30 2.540 1862.00 1850.00 61.28 435.339 56.50 17.168 63.33 64.85 24.927 Minimum Std. Deviation N Minimum Std. Deviation N Minimum Std. Deviation N Median Maximum N Median Maximum Median Maximum Median Maximum Median Maximum Minimum Std. Deviation N Minimum Std. Deviation LAYER BA_511P CO_ EMean SMean W I Mean W II Mean Total Mean Table 5. Trace element concentrations in different till beds and sediments, ppm.

33 Geological Survey of Finland, Special Paper 34 Esko Iisalo Fig. 4a. Concentrations of Cu, Zn, Ni and Ba in different till beds.

34 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... Fig. 4b. Concentrations of Sr, Ti and V in different till beds.

35 Geological Survey of Finland, Special Paper 34 Esko Iisalo

than in till beds WII and WI (Fig. 4). twice those in the till beds, whereas the concentration The average concentrations in the Eemian sedi- of strontium is only a little higher than in the till beds. ments containing abundant clay fraction are nearly

CHEMICAL CHARACTERISTICS OF TILL BEDS AND SEDIMENTS

The S till is characterized by a calcium concentration cantly higher than in other till beds. Its concentrations much higher than that of the other till beds. Its concen- of sodium and calcium are also higher than those of trations of sodium and phosphorus are also high, the WII till. Sporadically occurring high sulphur whereas it contains less aluminium, iron, manganese, concentrations are typical of this till. potassium and zinc than the other till beds (Fig. 5). Typical of the WII till are high concentrations of The WI till has a potassium concentration signifi- aluminium, iron and manganese, whereas the concen-

Fig. 5. Major element concentrations in different till beds.

36 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... trations of calcium, phosphorus and sulphur are low. beds. Phosphorus is a significant exception, with The concentrations of most major and trace ele- concentrations in the sediments lower than in the tills. ments in the Eemian sediments are 1.2-2 times higher The concentrations of calcium and strontium are also than in the till beds. The sulphur concentrations in the low, and rise only a little higher than in the till beds. sediments are many times as high as those of the till

EFFECT OF PARTICLE-SIZE DISTRIBUTION ON ELEMENT DISTRIBUTION

The correlation coefficients between the numerical The correlations between the amount of clay in the values that express the element distribution and fines and trace elements are strong for barium (0.73) particle-size distribution of the till samples are shown and cobalt (0.70), fairly strong for chromium (0.68), in Tables 6 and 7. These numerical values are D50, titanium (0.64), vanadium (0.62) and zinc (0.56), amount of fines and concentration of clay in the fines. and moderate for strontium (0.50), nickel (0.45) and The linear dependence is strong for correlation coef- copper (0.35). ficients > 0.7, moderate if the coefficient lies between The correlations between amount of fines in the till 0.7 and 0.3 and weak or negative where the coeffi- and concentration of trace elements are weak or cient is less than 0.3. negative. The greatest variations are found in the The correlations of both D50 value and the amount correlations with the D50 value. The correlations of fines with the major element concentrations are with nickel, copper and zinc are moderate, whereas weak or negative. Iron is an exception, showing a those with the other trace elements in Table 8 vary moderate correlation with the D50 value. from weak to negative. The clay proportions in the fines correlate best with The clay proportions in till samples clearly correlate the major elements. The elements with the strongest better with the element concentrations than do the correlations are manganese (0.58), iron, magnesium, average particle size and the amounts of fines. Also potassium and aluminium (> 0.54). The correlations in the Eemian sediments, the high concentrations of of sodium (0.50) and calcium (0.35) are somewhat elements are related to the high clay concentration. weaker, and the correlations of phosphorus (0.25) Exceptions are phophorus and calcium, the concen- and sulphur (0.10) with clay proportions are weak. trations of which are fairly low in the sediments.

Table 6. Correlations between concentrations of major elements Table 7. Correlations between concentrations of trace elements in till samples and quantities expressing particle-size distribution in till samples and quantities expressing particle-size distribution (D50, fines in till, clay concentration in fines). (D50, fines in till, clay concentration in fines).

CLAY_FIN FINES D50_MM CLAY_FIN FINES D50_MM

AL_511P .583 .021.191 BA_511P .765 .308 .055 CA_511P .380 .222 -.187 CO_511P .747 .307 .279 FE_511P .631.133.393 CR_511P .676 -.022 .286 K_511P .643 .319 .191 CU_511P .449 .204 .418 MG_511P .632 .174 .156 NI_511P .469 -.103 .583 MN_511P .661.376 .245 SR_511P .498 .098 -.204 NA_511P .591.376 -.013 TI_511P .644 .157 -.037 P_511P .145 -.158 -.042 V_511P .621-.074 .185 ZN_511P .633 .236 .396

DISCUSSION

Glaciation stages My results confirm the view that in Ostrobothnia sediments as shown in Figure 6. The particle-size three till beds occur, formed during different glacia- distribution and geochemical properties of the till tion stages but forming a continuous stratigraphic beds in the area are in agreement with results of earlier sequence at Mertuanoja in Ylivieska. These till beds studies, in which the tills of WI and WII were found are separated by esker formations and interglacial to represent the older and the younger glacial stage of

37 Geological Survey of Finland, Special Paper 34 Esko Iisalo

Fig. 6. The stratigraphic sequence of till beds, eskers and sediments in the study area according to this work. The interpretation of esker stratigraphy is based on observations made at Mertuanoja in Ylivieska (Iisalo 1996) and Vuojalankangas in Oulainen (Forsström 1982, Nenonen 1995).

the Weichselian ice age. the basis of their stratigraphic position. According to In terms of its properties and stratigraphic posi- Hytt et al. (1993) the OSL dates measured from Early tion the WI till resembles a till bed found in Sweden, Weichselian Brörup sand deposits in Ostro-bothnia which predates the Odderade interstadial and ex- belong to the age group 76-106 ka. The dates are tends from northern Sweden to south of Stockholm clearly older than the OSL dates 38-70 ka of littoral according to Lundqvist (1992). On the basis of its and glaciofluvial sands at Mertuanoja. Weichselian I till stratigraphic position till bed WI has been corre- is younger than Brörup interstadial and may have lated by Iisalo (1992) with the Early Weichselian till deposited during the early Weichselian 5b isotope of Lapland, described by Hirvas (1991). A different stadial 93000-85000 yr BP (Martinson et al. 1987, view has also been presented by Hirvas and Nenonen Mangerud 1991a,b) or/and during the Middle (1987), Sutinen (1992), and Nenonen (1995), sug- Weichselian 4 isotope stadial 74000-59000 yr BP. gesting that the distribution of the Early Weichselian The characteristics of the S till, which was de- till is limited to the area of Northern Finland. Nenonen scribed by Hirvas and Nenonen (1987) and which suggested that after the deposition of the Mertuanoja represents the Saalian glaciation, were also con- interstadial sediments, during the early part of the firmed and complemented. Mid-Weichselian, the continental ice sheet over- rode the deposits formed in Ostrobothnia during the Till bed S ice-free stage. Also according to Hytt et al. (1993) it has been concluded on the basis of litho- The properties of the Saalian till, which is lower- stratigraphical observations that only one till unit most in the stratigraphic sequence, are subject to covers the interglacial strata, although some indi- some uncertainty due to the small sample volumes. cations of two till units exist. The till is clearly coarser-grained than the overlying On the basis of stratigraphy, radiocarbon and Weichselian till, although the particle-size analyses OSL dating and the pollen spectrum, it is probable show the samples to be on the average sandy silt till. that the esker at Mertuanoja in Ylivieska and the Sandy till has also been observed in the area (Nenonen organic deposits found on the surface of the esker, 1992). The high concentrations of phosphorus, cal- were formed during the Middle-Weichselian or the cium and sodium in the till may partly stem from late Early-Weichselian (dating methods are not Eemian sediments and the Eemian biosphere, from exact)deglaciation and the following interstadial which they have been leached and precipitated in and should be correlated with the Peräpohjola the underlying till. The moderately high clay propor- (Korpela 1969) and Maaselkä (Hirvas 1991) de- tion in the fines may be partly due to weathering, posits of Lapland. On the other hand, the deposits which was intensified during the warm interglacial of the Brörup interstadial found underlying the and thus more advanced than in the other tills. Weichselian till in Ostrobothnia (e.g. Forsström Weathering of plagioclase increases the concentra- 1982, Gibbard et al. 1989) are older than these on tions of calcium and natrium.

38 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds...

Till bed W I area (Iisalo 1995), 1410 samples taken by percus- sion drill from various depths were used to show that The lower Weichselian I till, transported from the the 10-180 ppm sulphur concentrations measured in west-northwest, contains significantly more fines than the surface parts of the till suddenly increased many the upper Weichselian till, transported from the north- times to 400-800 ppm at a depth of 3-4 meters. In west. The boundary between these till beds is at an test pits dug above the groundwater table in the study average depth of 2.5 m, which is well above the area the boundary between the two uppermost till groundwater table at the study sites. The abundant beds lies at an average depth of three metres fines in the lower Weichselian till is due to Eemian (Kauranne 1979). It is thus probable that the raised sediments, which were mixed with the till during the sulphur concentrations are related to the lower initial stage of the Weichselian ice age. At the coast of Weichselian till. central Ostrobothnia, marine Eemian sediments Findings of interglacial pollen in the lower formed in saline water are found up to a level of 120 Weichselian till by Iisalo (1992) and in the fines- m above sea level according to Grönlund (1991). dominated basal till of Ostrobothnia by Heinonen The thickness of late glacial and postglacial sedi- (1957) also indicate that Eemian sediments have ments formed in the river valleys and bog basins of been mixed with the till. Ostrobothnia varies from a few metres to over ten metres. It can be assumed that the Eemian sediments Till bed WII attained similar thicknesses. Both Holocene and Eemian fines-dominated sediments consist mainly of Weathering and podzolization processes occur- silt and partly of clay. ring in oxidizing conditions have contributed to high The admixture of fines-dominated sediments has concentrations of aluminium, iron and manganese in not increased the element concentrations of the till. the Weichselian II till uppermost in the stratigraphic The silt fraction, which consists mainly of quartz and sequence. Concentrations of Al, Fe and Mn in feldspar, tends to dilute the concentrations whereas samples taken from the C horizon below the illuvial the clay fraction, which consists of clay minerals, horizon are lower than typical concentrations in the raises the concentrations. The fairly high potassium illuvial horizon (Räisänen 1996), but higher than concentrations in the till are an exception, due to those of the underlying till beds. In the light of these biotite, which is soluble in aqua regia (Räisänen et al. results it is possible that the precipitates are not 1992). Biotite is fairly abundant in the silt fraction. merely leached from the eluvial horizon by gravita- The markedly high sulphur concentrations in the tional waters. The drying of the fines-dominated till lower Weichselian I till are mainly caused by sulphur- during summertime causes the capillary rise of bearing Eemian sediments. By calculation it can be soluble aluminium, iron and manganese towards the shown that a one-meter thick sediment bed with a acidic surface layers until precipitation occurs in sulphur concentration of 1000-10000 ppm, mixed suitable pH-Eh conditions. This phenomenon re- with a four meter-thick till bed causes a rise in sulphur sembles processes that occur on a larger scale in arid concentration of 250-2500 ppm. These numbers are salt deserts and areas with alum earth or tropical in accord with the results of this study. The strong laterite soils (Uusinoka 1981). The rapid transport of deviation of the sulphur concentrations was due to readily soluble elements to greater depths with gravi- regional differences, since the sulphur-bearing sedi- tational water causes the surficial till to be depleted in ment sources are unevenly distributed. The second- calcium and phosphorus (Shilts & Kettles 1990, ary enrichment of sulphur is probably due to trans- Kujansuu 1981). portation by gravitational water seepage from the The glacial history has contributed to the coarse surface parts of the till to deeper-lying layers. The grain size and low sulphur concentration of the upper Saalian till clearly contains less sulphur than the Weichselian till. During deglaciation, which, in my lower Weichselian till. The position of the groundwa- opinion, occurred in supra-aquatic conditions during ter table does not seem to correlate with high sulphur the early Middle or late Early Weichselian, sand concentrations, as in the test pits the upper boundary deposits washed by glacial meltwaters were formed of the sulphide-bearing till extends several meters on the land surface, and during the Middle and Late above the groundwater table. In a study of the Vihanti Weichselian glaciation they were mixed with till.

39 Geological Survey of Finland, Special Paper 34 Esko Iisalo

During this interstadial with a cool climate, the sea during or after deposition. Sulphur concentrations in level was lower than at present, so no sulphur-bearing the Eemian sediments are many times those in till. The marine sediments could be deposited. Several lines of maximum concentration of 8090 ppm represents a evidence for this are the interstadial esker formations concentration level common in the postglacial sul- found in central Ostrobothnia (Iisalo 1992, 1996), phide clays of Ostrobothnia (Purokoski 1958). the pollen analyses,indicativeradiocarbon and OSL datings of their surficial parts (Iisalo 1992, Nenonen Effect of clay concentration 1995), the sand and soil horizon deposits found between till beds, and the conclusions of Lundqvist The amount of clay in the fine fraction has a (1992) and Lundqvist and Robertsson (1994) re- considerable effect on the element distributions of garding sea level during the Weichselian. single till samples. Since the average clay concentrations in the fines of various till beds are of the same Eemian sediments order of magnitude, significant differences in concentration between the till beds are unlikely to exist. The High element concentrations in the Eemian fine- regional differences in till fines content and clay grained sediments are related to high concentrations proportions in fine fractions found in earlier studies by of clay. The same phenomenon is shown by a com- Lintinen (1995) and Räisänen et al. (1992) are due to parative study of postglacial clays and till beds from other factors, including different degrees of washing southwestern Finland (Salminen et al.1997). Low and weathering of till beds, variations in glacial ero- concentrations of phosphorus and calcium in Eemian sion and contrasting bedrock types and weathering. sediments may be due to solution that has occurred

CONCLUSIONS

The results of this study confirm the earlier conclu- The average WI till is significantly finer-grained than sion (Iisalo 1992, 1996), that three till beds, depos- the WII till. Abundant silt in the lower WI till is due to ited during different glacial stages, occur in the mixing of Eemian fine-grained sediments with the Ostrobothnia. At Mertuanoja in Ylivieska, these till till, however the admixture of fines-dominated sedi- beds form a continuous stratigraphic sequence, in ments has not raised the element concentrations of which they are separated by interstadial and intergla- the till. The silt fraction, comprising mainly quartz and cial eskers and sediments. feldspar, tends to dilute the concentrations while the Lowermost in the sequence is the Saalian S till, clay fraction, made up ofclay minerals readily soluble which contains less fine fraction than the Weichselian in aqua regiaincreases concentrations.The potas- WI till overlying it. The proportion of clay fraction in sium concentration indicated by micas, is significantly the fines of the S till is somewhat higher than in the higher than in other till beds.The concentrations of other till beds, although the differences are not signifi- sodium and calcium are also higher than in the WII till. cant. On average the S till is a sandy silt till. Coarse- The till is characterized by high sulphur concentra- grained sandy tills are also found in the study area. tions, due mainly to the mixing of sulphur-rich Eemian The S till fines is characterized by calcium concentra- sediments into the till. tions clearly higher than in the other till beds. It is also Compared with WI till, the WII till is coarser- high in sodium and phosphorus, but contains less grained and clearly contains less fine fraction. The aluminium, iron, manganese, potassium, copper and WII till is dominated by sand and silty sand. Its zinc than the others. All the concentrations in this concentrations of aluminium, iron and manganese are study are based on the aqua regia partial analyses. typically high, whereas it is relatively low in calcium, A high proportion of fines is a typical feature of the phosphorus and sulphur. Podzolisation and oxidis- WI till. Due to the high silt concentration the propor- ation involves enrichment of iron and aluminium in the tion of clay in the fines is no higher than in the other till surface layers of sandy till. The differences in par- beds although the amount of clay in the till as a whole ticle-size distributions and element concentrations is higher than in the upper WII till and the lower S till. between the lower and upper Weichselian tills were

40 Geological Survey of Finland, Special Paper 34 Till stratigraphy and geochemical differences between till beds... considered to be partly due to deglaciation, which considerable importance for the element concentra- occurred in supra-aquatic conditions, and the follow- tions in single samples of normal till. The clay abun- ing interstadial, the exact age of which around the dances of whole till samples have strong correlations Mid-Weichselian glaciation has not been possible to with the elements barium, cobalt, chromium and determine. manganese, which originate mica and clay minerals The fines of the Eemian sediments contain an readily soluble in aqua regia.The correlations with average of 27% clay, while the bulk (73%) of the copper, calcium, sulphur and phosphorus were found sediment is silt. The concentration of clay fraction is to be weak or moderate. Correlations with other nearly double that found in the till beds. The concen- elements were classified as moderate. The high trations of most major and trace elements in the element concentrations in the Eemian sediments are Eemian sediments are 1.5-2 times as high as in the till also due to high clay fraction abundances. beds. The sulphur concentrations in the sediment are High clay contents cause a rise in background many times those in the till. Phosphorus is a significant values in element maps based on till fines. However, exception, with concentrations in the sediments lower these changes in concentrations are small compared than in the till. The concentrations of calcium are also with the changes caused by the rock types of the low, rising only a little higher than in the till beds. bedrock. The study did not deal with regional con- Since the proportion of clay in the fine fraction is of centration variations caused by the bedrock, the the same order in all the till beds studied, it does not magnitude of which is generally many times that of cause any significant variations in average concentra- anomalies caused by differences between till beds in tions of the elements between the till beds. However, particle-size distribution and depositional conditions. the abundance of clay in the fine fraction of till is of

Acknowledgements

I would like to thank Dr Marja Liisa Räisänen, script and Heli Moberg for drawing the figures. The Professor Matti Eronen and Aimo Hartikainen for manuscript was translated into English by Carola their suggestions and critical review of the manu- Eklundh.

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