Working Report 2009-25 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-27160 EURAJOKI, FINLAND Tel +358-2-8372 31 Fax +358-2-8372 3709
Working Report 2009-25 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.
ABSTRACT The Quaternary deposits in investigation trenches OL-TK15 and OL-TK16 were studied by the Geological Survey of Finland in summer 2008. 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 0.002 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
Maaperätutkimukset tutkimuskaivannoissa OL-TK15 ja OL-TK16 Olkiluodon alueella Eurajoella Lounais-Suomessa TIIVISTELMÄ Olkiluodon tutkimuskaivannot OL-TK15 ja OL-TK16 tutkittiin kesällä 2008. 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
1 TABLE OF CONTENTS ABSTRACT TIIVISTELMÄ 1 INTRODUCTION... 3 2 SAMPLING AND GRAIN SIZE DETERMINATIONS... 5 3 RESULTS OF INVESTIGATION... 7 4 SUMMARY... 13 REFERENCES... 15 APPENDICES... 17
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3 1 INTRODUCTION The Quaternary deposits in investigation trenches OL-TK15 and OL-TK16 were studied by the Geological Survey of Finland in summer 2008. 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-TK15-01 05 and OL-TK16-01 - 08. 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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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-TK15 01 0-1.8 silty till silty till OL-TK15 02 0-2.0 sandy till fine sandy till OL-TK15 03 0-1.0 silty till fine sandy till OL-TK15 03 1.0-4.0 silty till fine sandy till OL-TK15 04 0-2.0 sandy till fine sandy till OL-TK15 04 2.0-3.0 silty till fine sandy till OL-TK15 05 0-2.4 silty till fine sandy till OL-TK15 05 2.4-4.0 silty till fine sandy till OL-TK16 01 0-1.2 sandy till fine sandy till OL-TK16 02 0.4-1.4 sandy till fine sandy till OL-TK16 03 0.2-1.4 sandy till fine sandy till OL-TK16 04 0.2-0.8 sandy till fine sandy till OL-TK16 04 0.8-1.6 silty till fine sandy till OL-TK16 05 0.2-0.8 silty till fine sandy till OL-TK16 05 0.8-1.2 silty till fine sandy till OL-TK16 05 1.2-2.0 sandy till fine sandy till OL-TK16 06 1.6-2.4 silty till fine sandy till OL-TK16 06 2.4-3.0 silty till fine sandy till OL-TK16 07 0-1.4 silty till fine sandy till OL-TK16 07 1.4-3.4 silty till fine sandy till/silty till OL-TK16 08 0-1.4 silty till fine sandy till OL-TK16 08 1.4-3.2 silty till fine sandy till Soil type classification after Aaltonen et al. 1949 (RT) and Korhonen et al. 1974 (GEO).
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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 15-01 05. 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 0.002 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.
8 Figure 2. Upper till in OL-TK 15-01. 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.
9 Figure 3. Summary of sampling profiles OL-TK 16-01 08. 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).
10 Figure 4. Dark grey till and a channel filled with sand/clay in OL-TK 16 06. 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 0.002 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).
11 Figure 5. Sand filled cracks in dark grey till in OL-TK16 07. 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 30 000-10 000 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 70 000-36 000 BP. The till contains pollen and diatom from the sea sediments (clays) formed during the Eemian interglacial period (130 000-115 000 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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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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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., 1949. Maaperäsanaston ja maalajien luokituksen tarkastus v. 1949. Summary: A critical review of soil terminology and soil classification in Finland in the year 1949. Maataloustieteellinen Aikakauskirja: 21, 37 66. Hirvas, H., 1991. Pleistocene stratigraphy of Finnish Lapland. Geological Survey of Finland, Bulletin 354. 123 p., 75 figs., 9 tables and 2 appendices. Huhta, 2008. Studies of Quaternary Deposits of Investigation Trench OL-TK14 at the Olkiluoto Study Site, Eurajoki, SW Finland. Working Report 2008-31. Posiva. Korhonen, K.-H., Gardemeister, R. & Tammirinne, M., 1974. Geotekninen maalajiluokitus. Geotekniikan laboratorio, tiedonanto 14, 20 s. 2 liitettä.
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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 TK16/01-08. Appendix 4 16. Field observation forms OL-TK15/01 05 and TK16/01-08. Appendix 17 38. Grain size analyses from trenches OL- TK15 and TK16.
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19 Appendix 1. Coordinates (KKJ) of the soil sampling profiles in trenches OL-TK15 and TK16. Profile x y z OL-TK15-01 6791792 1527713 1.1 OL-TK15-02 6791768 1527712 1.9 OL-TK15-03 6791746 1527707 3.7 OL-TK15-04 6791719 1527703 4.1 OL-TK15-05 6791702 1527702 4.2 OL-TK16-01 6791719 1527516 4.7 OL-TK16-02 6791716 1527541 4.5 OL-TK16-03 6791708 1527562 5.0 OL-TK16-04 6791703 1527586 5.2 OL-TK16-05 6791700 1527612 4.7 OL-TK16-06 6791697 1527637 2.9 OL-TK16-07 6791692 1527663 2.9 OL-TK16-08 6791689 1527682 2.2 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 2-0.6 sand sand 0.6-0.2 sand sand 0.2-0.06 sand fine sand 0.06-0.02 silt fine sand 0.02-0.006 silt silt 0.006-0.002 silt silt under 0.002 clay clay
20 Appendix 2. Location of investigation trenches OL-TK14, OL-TK15 and OL-TK16.
21 Appendix 3. Location of sampling profiles OL-TK15-01 05 and TK16-01 - 08.
22 Appendix 4
23 Appendix 5
24 Appendix 6
25 Appendix 7
26 Appendix 8
27 Appendix 9
28 Appendix 10
29 Appendix 11
30 Appendix 12
31 Appendix 13
32 Appendix 14
33 Appendix 15
34 Appendix 16
35 Appendix 17
36 Appendix 18
37 Appendix 19
38 Appendix 20
39 Appendix 21
40 Appendix 22
41 Appendix 23
42 Appendix 24
43 Appendix 25
44 Appendix 26
45 Appendix 27
46 Appendix 28
47 Appendix 29
48 Appendix 30
49 Appendix 31
50 Appendix 32
51 Appendix 33
52 Appendix 34
53 Appendix 35
54 Appendix 36
55 Appendix 37
56 Appendix 38