Studies of Quaternary Deposits of Investigation Trench OL-TK14 at the Olkiluoto Study Site, Eurajoki, SW Finland

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1 Working Report Studies of Quaternary Deposits of Investigation Trench OL-TK14 at the Olkiluoto Study Site, Eurajoki, SW Finland Pekka Huhta Geological Survey of Finland May 2008 Base maps: National Land Survey, permission 41/MYY/08 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.

2 ABSTRACT The Quaternary deposits in investigation trench OL-TK14 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, 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 on a field observation form and the profiles were photographed using a digital camera. In addition, the excavated section was photographed along almost their whole length. The till cover in OL-TK14 consist of two parts. The surface layer of the upper till is oxidized, brown sandy till, whereas the lower layer is unoxidized, grey sandy till. The thickness of the upper till varies from 1.0 to 3.7 meters. The upper till has a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. The upper till has normal compactness. The lower till has been preserved in bedrock depressions and fragments of it s material has ascended the upper till. The lower till is compact, dark grey silty till with more than 15 % of fine material (under mm). The lower till has a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. The upper till in OL-TK14 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. Broken bedrock was found in the eastern part of OL-TK14 at bottom of sampling profiles TK14-06 and TK The surface of broken bedrock was strongly weathered and reddish brown in colour. Lowest part of till material has mixed to it forming layer of weathered bedrock till. The dark grey silty till above broken bedrock has been vertically cracked forming a netlike pattern. The cracks are filled with sand. This cracking and sand filling is possibly happened by ice pressure when the ice was depositing the upper sandy till. This cracking has only happened over the broken bedrock. 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 over broken bedrock. Keywords: overburden, glacial geology, till, stratigraphy, trench, grain size, Quaternary, Finland; Western Finland Province; Satakunta; Eurajoki; Olkiluoto

3 Maaperätutkimukset tutkimuskaivannossa OL-TK14 Olkiluodon alueella Eurajoella Lounais-Suomessa TIIVISTELMÄ Olkiluodon tutkimuskaivanto OL-TK14 tutkittiin kesällä Kaivannosta 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 tutkimuskaivanto kuvattiin kameralla lähes päästä päähän. TK14:sta löydettiin kahden eri jäätiköitymisvaiheen moreenipatjat. Ylempi moreeni koostuu kahdesta kerroksesta. Pintaosassa on hapettunut, ruskea hiekkamoreeni. Alempi kerros on hapettumaton, harmaa hiekkamoreeni. Ylemmän moreenipatjan paksuus vaihtelee 1,0:sta 3,7:een metriin. Moreeni on tiiviydeltään ja kivisyydeltään normaalia hiekkamoreenia, jossa keskimääräinen kivikoko vaihtelee 6-60 senttimetriin ja kiviaines on kulmistaan pyöristynyttä. Alempi moreenipatja on säilynyt kallion painanteissa. Kappaleita sen pinnasta on kulkeutunut ylempään moreeniin. Alempi moreeni on tiivistä, tummanharmaata silttimoreenia, jossa savespitoisuus (<0.002 mm:n ainesta) on yli 15%, kun sitä ylemmässä moreenissa on normaalisti alle 10%. Alemman moreenin kivisyys on vähäisempi kuin ylemmän ja kivikoko vaihtelee 6-60 senttimetriin. Kiviaines on kulmistaan pyöristynyttä. Ylemmän moreenin kerrostanut jäätikkö on uurresuuntien perusteella virrannut länsiluoteesta itäkaakkoon. Maastossa moreenipeite tasoittaa kalliopinnan epätasaisuudet. Rikkonaista kalliota löytyi tutkimuskaivannon OL-TK14:n itäpäästä näytteenottoprofiilien TK14-06 ja TK14-07 pohjalta. Rikkoutuneen kallioperän pintaosa oli voimakkaasti rapautunutta. Moreenin alaosa on sekoittunut rapakalliomateriaaliin muodostaen rapakalliomoreenikerroksen, jossa on runsaasti savifraktiota hiekkamoreenissa (yli 24 %). Rikkoutuneen kallion yläpuolella oleva silttimoreeni on pystysuoraan rakoutunut muodostaen verkkomaisen kuvioituksen. Raot ovat täyttyneet hiekalla. Tämä rakoilu lienee tapahtunut jäätikön paineen voimasta ylemmän hiekkamoreenin kerrostumisen aikana. Rakoilua silttimoreenissa havaittiin vain rikkonaisen kallion päällä. 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

4 1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ 1 INTRODUCTION SAMPLING AND GRAIN SIZE DETERMINATIONS RESULTS OF INVESTIGATION SUMMARY REFERENCES... 8 APPENDICES... 9

5 2 1 INTRODUCTION The Quaternary deposits in investigation trench OL-TK14 were studied by the Geological Survey of Finland in summer The investigations were carried out in three 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 on a field observation form and the profiles were photographed using a digital camera except TK14-09, which was studied week after the other profiles. In addition, the excavated section was photographed almost along the whole length. Sampling profiles are numbered as OL-TK The coordinates of sampling profiles are in Appendix 1 and the locations in Appendices 2 and 3. The location of each sampling profile was determined with the help of pre-determined starting and end points of sections for bedrock mapping. Observation forms and grain size analyses of each profile are in Appendices of this report.

6 3 2 SAMPLING AND GRAIN SIZE DETERMINATIONS Samples for grain size determinations were taken from vertical profiles extending from the soil surface down to bedrock. Between 3 and 4 kg of sediment was taken in a bucket 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 soil type classification in OL- TK 14. Table 1. Soil sampling depths and soil type classification in OL-TK 14. Profile TK14-01 TK14-01 TK14-02 TK14-03 TK14-04 TK14-05 TK14-06 TK14-06 TK14-06 TK14-07 TK14-07 TK14-07 TK14-08 TK14-08 TK14-09 TK14-09 depth in metres Soil type classification d50 (GEO) geotechnical classification (RT) sandy till fine sandy till silty till fine sandy till sandy till fine sandy till sandy till fine sandy till sandy till fine sandy till silty till fine sandy till sandy till fine sandy till silty till fine sandy till sandy till fine sandy till (clay content 24.2%) sandy till fine sandy till (clay content 15.5%) silty till fine sandy till sandy till fine sandy till (clay content 24.7%) sandy till fine sandy till sandy till fine sandy till sandy till fine sandy till sandy till fine sandy till Soil type classification after Aaltonen et al (RT) and Korhonen et al (GEO).

7 4 3 RESULTS OF INVESTIGATION The length of OL-TK 14 is approximately 215 m and 9 profiles were sampled from it. The height of the profiles varied from 4.9 m to 1.4 m with an average of 2.9 m. 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 the sampling profiles OL-TK The till cover in OL-TK14 consist of two parts. The upper till has two layers. Surface layer is oxidized, brown sandy till. The lower layer is unoxidized, grey sandy till. The thickness of the upper till varies from 1.0 to 3.7 meters. The upper till in OL-TK14 is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded. The upper till has normal compactness (Fig. 2). The lower till has been preserved in bedrock depressions. Part of it s material has ascended the upper till. The lower till is compact, dark grey silty till with over 15 % of fine material (under mm). The lower till is classified as having a normal amount of cobbles and boulders with the size of the larger clasts varying from 6 to 60 cm. The edges of clasts have been eroded and rounded (Fig. 2). The upper till bed in OL-TK14 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 during an earlier flow phase of the Weichselian continental ice.

8 5 Figure 2. Upper and lower till in OL-TK Broken bedrock was found in the eastern part of OL-TK14 at bottom of sampling profiles TK14-06 and TK The surface of broken bedrock was strongly weathered and reddish brown in colour (Fig 3). Lowest part of till material has mixed to it forming layer of weathered bedrock till. This sandy reddish brown till contains plenty of clay size material from the weathered bedrock (over 24 %). Till is quite thin, only 0.2 to 0.4 meters. Figure 3. Wheathered bedrock in OL-TK14 07.

9 6 The dark grey silty till above broken bedrock has been cracked vertically forming a netlike pattern. The cracks are filled with sand (Fig. 4). This cracking and sand filling is possibly caused by ice pressure when the ice was depositing the upper sandy till. This cracking has only happened over the broken bedrock. 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 over the broken bedrock. Figure 4. Sand filled crack in dark grey silty till. The phone is 11 cm long.

10 7 4 SUMMARY Two till beds were found in trench OL-TK14 in Olkiluoto. The upper till bed has two layers. Surface layer is oxidized, brown sandy till, whereas the lower layer is unoxidized, grey sandy till. The lower till bed has been preserved in bedrock depressions. It is compact, dark grey silty till with over 15 % of fine material (under mm). The upper till bed in OL-TK14 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. Broken bedrock was found in the eastern part of OL-TK14. The surface of broken bedrock was strongly weathered. Lowest part of till material has mixed to it forming layer of weathered bedrock till. This sandy till contains plenty of clay size material from the weathered bedrock (over 24 %). The dark grey silty till above broken bedrock has been cracked vertically and the cracks are filled with sand. This cracking and sand filling is possibly happened when the ice was depositing the upper sandy till and pressed the lower till. This cracking has only happened over the broken bedrock. 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 over broken bedrock.

11 8 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, Korhonen, K.-H., Gardemeister, R. & Tammirinne, M., Geotekninen maalajiluokitus. Geotekniikan laboratorio, tiedonanto 14, 20 s. 2 liitettä.

12 9 APPENDICES Appendix 1. Coordinates of the soil sampling profiles in trench OL-TK14. Appendix 2. Location of investigation trench OL-TK14. Appendix 3. Location of sampling profiles OL-TK14/ Appendix Field observation forms OL-TK14/ Appendix Grain size analyses from samples OL-TK14/01 09.

13 10 Appendix 1. Coordinates of the soil sampling profiles in trench OL-TK14. Profile x y z TK14-01 TK14-02 TK14-03 TK14-04 TK14-05 TK14-06 TK14-07 TK14-08 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