Studies of Quaternary Deposits in Investigation Trenches OL-TK15 and OL-TK16 on the Olkiluoto Study Site, Eurajoki, SW Finland. Working Report

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1 Working Report Studies of Quaternary Deposits in Investigation Trenches OL-TK15 and OL-TK16 on the Olkiluoto Study Site, Eurajoki, SW Finland Pekka Huhta May 2009 POSIVA OY Olkiluoto FI EURAJOKI, FINLAND Tel Fax

2 Working Report Studies of Quaternary Deposits in Investigation Trenches OL-TK15 and OL-TK16 on the Olkiluoto Study Site, Eurajoki, SW Finland Pekka Huhta Geological Survey of Finland May 2009 Base maps: National Land Survey, permission 41/MML/09 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva.

3 ABSTRACT The Quaternary deposits in investigation trenches OL-TK15 and OL-TK16 were studied by the Geological Survey of Finland in summer Samples for grain size determinations were taken from vertical profiles, placed 25 m apart along the trench. Each till bed was sampled separately. The profiles extended from the soil surface down to bedrock. The samples were first dried in the laboratory after which they were sieved. In addition, the grain size distribution of the < 63 µm fraction was analyzed with the Sedigraph 5100 instrument. Sedimentological observations of the sampling profiles were documented in field by drawing them on a field observation form and the profiles were photographed using a digital camera. In addition, the excavated section was photographed along its whole length. The till cover in OL-TK15 and OL-TK16 consists of two parts. The surface layer of the upper till is oxidized, brown till, whereas the lower layer is unoxidized, grey till. The lower till has been preserved in bedrock depressions. The lower till is compact, dark grey silty till with more than 20% of clay-size material (under mm). The upper till in OL-TK15 and OL-TK16 was deposited in the last flow phase of the Weichselian continental ice. Bedrock striations indicate that the ice moved in a WNW- ESE direction. The till beds level out the bedrock topography. Weathered bedrock till, and also weathered bedrock, was found in places at the bottom of both trenches. The dark grey silty till in profile OL-TK16-07 is vertically cracked. The cracks are filled with sand. This cracking and sand filling has possibly been caused by ice pressure when ice deposited the upper till. No broken bedrock was found under the cracked till as in trench OL-TK14. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements, only icepressed cracks were found in the lower silty compact till. Keywords: overburden, glacial geology, till, stratigraphy, trench, grain size, Quaternary, Finland; Province of Western Finland; Satakunta; Eurajoki; Olkiluoto

4 Maaperätutkimukset tutkimuskaivannoissa OL-TK15 ja OL-TK16 Olkiluodon alueella Eurajoella Lounais-Suomessa TIIVISTELMÄ Olkiluodon tutkimuskaivannot OL-TK15 ja OL-TK16 tutkittiin kesällä Kaivannoista otettiin lapiolla raesuuruusnäytteet 25 metrin välein vertikaalisesti läpi koko moreenipeitteen kallioon asti. Näytteet otettiin jokaisesta moreeniyksiköstä erikseen. Laboratoriossa näytteet kuivattiin, jonka jälkeen ne seulottiin. Seulottu alle 63 mikronin osanäyte analysoitiin Sedigraph 5100-laitteella. Jokainen näytteenottoprofiili kuvattiin piirtämällä lomakkeelle ja digitaalikameralla. Lisäksi tutkimuskaivannot kuvattiin kameralla päästä päähän. Tutkimuskaivannoista OL-TK15 ja OL-TK16 löydettiin kahden eri jäätiköitymisvaiheen moreenipatjat. Ylempi moreeni koostuu kahdesta kerroksesta. Pintaosassa on hapettunut, ruskea hiekka/silttimoreeni. Alempi kerros on hapettumaton, harmaa hiekka/silttimoreeni. Alempi moreenipatja on säilynyt kallion painanteissa. Alempi moreeni on tiivistä, tummanharmaata silttimoreenia, jossa savespitoisuus (<0.002 mm:n ainesta) on yli 20%. Ylemmän moreenin kerrostanut jäätikkö on uurresuuntien perusteella virrannut länsiluoteesta itäkaakkoon. Maastossa moreenipeite tasoittaa kalliopinnan epätasaisuudet. Rapakalliomoreenia löytyi molempien tutkimuskaivantojen pohjalta. Rapakalliota löytyi myös paikoin. Profiilissa OL-TK16-07 oleva silttimoreeni on pystysuoraan rakoutunut. Raot ovat täyttyneet hiekalla. Tämä rakoilu lienee tapahtunut jäätikön paineen voimasta ylemmän moreenin kerrostumisen aikana. Rakoilleen moreenin alta ei löytynyt rikkoutunutta kalliota kuten kaivannossa OL-TK14. Mitään merkkejä postglasiaalisista siirroksista ei moreenipeitteestä tai paljastetusta kallion pinnasta löydetty, eikä moreenissa havaittu kallioperän liikuntoihin viittaavia häiriörakenteita, vain jäätikön paineen tekemiä rakoja alemmassa silttimoreenissa. Avainsanat: maapeite, glasiaaligeologia, moreeni, stratigrafia, kaivannot, raekoko, kvartääri, Suomi; Länsi-Suomen lääni; Satakunta; Eurajoki; Olkiluoto

5 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ 1 INTRODUCTION SAMPLING AND GRAIN SIZE DETERMINATIONS RESULTS OF INVESTIGATION SUMMARY REFERENCES APPENDICES... 17

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7 3 1 INTRODUCTION The Quaternary deposits in investigation trenches OL-TK15 and OL-TK16 were studied by the Geological Survey of Finland in summer The investigations were carried out in two phases as the excavation progressed. Samples for grain size determinations were taken from vertical profiles, placed 25 m apart along the trench. Sedimentological observations of the sampling profiles were documented in field by drawing them on a field observation form and the profiles were photographed using a digital camera. In addition, the excavated section was photographed along the whole length. Sampling profiles are numbered OL-TK and OL-TK The coordinates of the sampling profiles are shown in Appendix 1 and the locations in Appendices 2 and 3. The location of each sampling profile was determined with the help of start and end points of sections pre-determined for bedrock mapping. The observation forms and the grain size analyses of each profile are presented in the Appendices of this report. An observation form is designed to standardize the recording of field data. Till properties (compactness, stone content, stone size, roundness of clasts) are classified on a five degree scale, on which 1 refers to the lowest and 5 to the highest degree of the property ( Hirvas 1991).

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9 5 2 SAMPLING AND GRAIN SIZE DETERMINATIONS Samples for grain size determinations were taken from vertical profiles extending from the soil surface down to bedrock. An amount of 3 to 4 kg of sediment was taken with a shovel and placed in plastic bags for transport to the laboratory. The samples were first dried in the laboratory. Grains over 6 mm were extracted before analysis. The samples were first sieved and then the grain size distribution of the < 63 µm fraction was analyzed with the Sedigraph 5100 instrument. Table 1 shows the soil sampling depths and the soil type classification in OL- TK 15 and OL-TK16. Table 1. Soil sampling depths and soil type classification in OL-TK 15 and OL-TK16. Profile depth in Soil type classification metres d50 (GEO) geotechnical classification (RT) OL-TK silty till silty till OL-TK sandy till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK sandy till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK sandy till fine sandy till OL-TK sandy till fine sandy till OL-TK sandy till fine sandy till OL-TK sandy till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK sandy till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till OL-TK silty till fine sandy till/silty till OL-TK silty till fine sandy till OL-TK silty till fine sandy till Soil type classification after Aaltonen et al (RT) and Korhonen et al (GEO).

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11 7 3 RESULTS OF INVESTIGATION A total of 5 profiles from north to south were sampled from OL-TK15, which is approximately 90 m long. The height of the profiles varied between 4.0 m and 1.8 m with an average of 3.0 m. A summary of the sampling profiles is presented in Fig. 1. The Figure shows how the till cover very effectively levels out the bedrock topography. Figure 1. Summary of sampling profiles OL-TK The till cover in OL-TK15 consists of two parts. The upper till has two layers. The surface layer is oxidized, brown sandy/silty till. The lower layer is unoxidized, grey sandy/silty till. The thickness of the upper till ranges from 1.0 to 4.0 meters. The upper till in OL-TK15 is classified as having a less than normal amount of cobbles and boulders, with the size of the larger clasts ranging from 6 to 20 cm. The edges of the clasts are eroded and rounded. The upper till displays normal compactness (Fig. 2). The lower till has been preserved in bedrock depressions. The lower till is compact, dark grey silty till with over 17 % of fine material (under mm). The lower till is classified as having a less than normal amount of cobbles and boulders, with the size of the larger clasts ranging from 6 to 20 cm. The edges of the clasts are eroded and rounded.

12 8 Figure 2. Upper till in OL-TK A total of 8 profiles from west to east were sampled from OL-TK16, which is approximately 170 m long. The height of the profiles varied between 3.4 m and 1.2 m with an average of 2.2 m. A summary of the sampling profiles is presented in Fig. 3.

13 9 Figure 3. Summary of sampling profiles OL-TK The till cover in OL-TK16 also consists of two parts. In places the upper till has two layers. The surface layer is oxidized, brown sandy/silty till. The lower layer is unoxidized, grey sandy/silty till. The thickness of the upper till ranges from 0.8 to 4.0 metres. The upper till in OL-TK16 is classified as having a less than normal amount of cobbles and boulders, with the size of the larger clasts ranging from 6 to 20 cm. The edges of the clasts are eroded and rounded. The upper till displays normal compactness (Fig. 4).

14 10 Figure 4. Dark grey till and a channel filled with sand/clay in OL-TK At profile OL-TK16-06 the upper till has been washed away to lower till forming some kind of a channel in it. This channel is filled with clay and sand. Sand was also found on the surface of the upper till. The lower till has been preserved in bedrock depressions. The lower till is compact, dark grey silty till with over 22 % of clay-size material (under mm). The lower till is classified as having a less than normal amount of cobbles and boulders, with the size of the larger clasts ranging from 6 to 20 cm. The edges of the clasts are eroded and rounded. The dark grey silty till in profile OL-TK16-07 is vertically cracked. The cracks are filled with sand. This cracking and sand filling has possibly been caused by ice pressure when ice deposited the upper till. No broken bedrock was found under the cracked till as in trench OL-TK14 (Huhta 2008).

15 11 Figure 5. Sand filled cracks in dark grey till in OL-TK The tool is 24 cm long. The lowest part of the till material has in both trenches been mixed with weathered bedrock material at some points, forming a layer of weathered bedrock till. This silty/sandy reddish brown till contains plenty of clay size material from the weathered bedrock (over 23 %). The thickness of this till is 0.2 to 0.8 metres. Weathered bedrock was found at some points at the bottom of both trenches. The upper till bed was deposited in the last flow phase of the Weichselian continental ice about BP. The lower till bed has been deposited in an earlier flow phase of the Weichselian. This dark grey silty till can be found widely in southwestern Finland and the estimated age of the till bed is about BP. The till contains pollen and diatom from the sea sediments (clays) formed during the Eemian interglacial period ( BP). Bedrock striations at the trench indicate that the ice moved in a WNW-ESE direction when the upper till bed was deposited. It has been measured earlier e.g. in OL-TK13 that during the deposition of the lower till bed the ice moved from North. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements, only icepressed cracks were found in the lower silty compact till.

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17 13 4 SUMMARY Two till beds were found in trenches OL-TK15 and TK16 in Olkiluoto. The upper till bed has two layers. The surface layer is oxidized, brown sandy/silty till, whereas the lower layer is unoxidized, grey sandy/silty till. These tills have an average clay-size fraction of 8 %. The lower till bed has been preserved in bedrock depressions. It is compact, dark grey silty till with 23 % of clay-size material on average. The upper till bed was deposited in the last flow phase of the Weichselian continental ice. Bedrock striations indicate that the ice moved in a WNW-ESE direction. The lower till bed has been deposited in an earlier flow phase of the Weichselian. The lowest part of till material has in both trenches mixed with weathered bedrock material at some points, forming a layer of weathered bedrock till. This silty/sandy reddish brown till contains plenty of clay size material (27 % on average) from the weathered bedrock. Weathered bedrock was found at some points at the bottom of both trenches. The dark grey silty till in profile OL-TK16-07 is vertically cracked. The cracks are filled with sand. This cracking and sand filling has possibly been caused by ice pressure when ice deposited the upper till. No broken bedrock was found under the cracked till as in trench OL-TK14. No signs of postglacial faults were detected either in the tills or in the exposed bedrock. The tills showed no signs of disturbance related to bedrock movements, only ice pressed cracks were found in the lower silty compact till.

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19 15 REFERENCES Aaltonen, V.T., Aarnio, B., Hyyppä, E., Kaitera, P., Keso, L., Kivinen, E., Kokkonen, P., Kotilainen, M.J., Sauramo, M., Tuovila, P. & Vuorinen, J., Maaperäsanaston ja maalajien luokituksen tarkastus v Summary: A critical review of soil terminology and soil classification in Finland in the year Maataloustieteellinen Aikakauskirja: 21, Hirvas, H., Pleistocene stratigraphy of Finnish Lapland. Geological Survey of Finland, Bulletin p., 75 figs., 9 tables and 2 appendices. Huhta, Studies of Quaternary Deposits of Investigation Trench OL-TK14 at the Olkiluoto Study Site, Eurajoki, SW Finland. Working Report Posiva. Korhonen, K.-H., Gardemeister, R. & Tammirinne, M., Geotekninen maalajiluokitus. Geotekniikan laboratorio, tiedonanto 14, 20 s. 2 liitettä.

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21 17 APPENDICES Appendix 1. Coordinates of the soil sampling profiles in trenches OL-TK15 and OL-TK16. Appendix 2. Location of investigation trenches OL-TK15 and TK16. Appendix 3. Location of sampling profiles OL-TK15/01 05 and TK16/ Appendix Field observation forms OL-TK15/01 05 and TK16/ Appendix Grain size analyses from trenches OL- TK15 and TK16.

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23 19 Appendix 1. Coordinates (KKJ) of the soil sampling profiles in trenches OL-TK15 and TK16. Profile x y z OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK OL-TK Notes for field observation forms: GS = sample for grain size analysis CO = compactness ST = stone content SSZ = stone size RO = roundness of clasts WB = weathered bedrock WBtill = till material mixed with WB Used grain diameters in mm: grain diameter mm geotechnical (geo) construction technical (rt) classification 20-2 gravel gravel sand sand sand sand sand fine sand silt fine sand silt silt silt silt under clay clay

24 20 Appendix 2. Location of investigation trenches OL-TK14, OL-TK15 and OL-TK16.

25 21 Appendix 3. Location of sampling profiles OL-TK and TK

26 22 Appendix 4

27 23 Appendix 5

28 24 Appendix 6

29 25 Appendix 7

30 26 Appendix 8

31 27 Appendix 9

32 28 Appendix 10

33 29 Appendix 11

34 30 Appendix 12

35 31 Appendix 13

36 32 Appendix 14

37 33 Appendix 15

38 34 Appendix 16

39 35 Appendix 17

40 36 Appendix 18

41 37 Appendix 19

42 38 Appendix 20

43 39 Appendix 21

44 40 Appendix 22

45 41 Appendix 23

46 42 Appendix 24

47 43 Appendix 25

48 44 Appendix 26

49 45 Appendix 27

50 46 Appendix 28

51 47 Appendix 29

52 48 Appendix 30

53 49 Appendix 31

54 50 Appendix 32

55 51 Appendix 33

56 52 Appendix 34

57 53 Appendix 35

58 54 Appendix 36

59 55 Appendix 37

60 56 Appendix 38