Workreport 2010-40

Studies of Quaternary Deposits in Investigation Trench OL-TK17 on the Olkiluoto Study Site, Eurajoki, SW Finland

Huhta, P.

English

62

The Quaternary deposits in investigation trench OL-TK17 were studied by the Geological Survey of Finland in summer 2009. Samples for grain size determinations were taken from 13 vertical profiles, placed about 25 m apart along the trench, where bedrock didn’t reach surface. Profiles 5 and 6 were done by the side of the trench because of that. 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-TK17 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 19 % of clay-size material (under 0.002 mm).

The upper till in OL-TK17 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, broken bedrock was found in two places at the bottom of the trench near sampling profiles 08, 09 and 10.

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.

overburden, glacial geology, till, stratigraphy, trench, grain size, Quaternary, Finland; Province of Western Finland; Satakunta; Eurajoki; Olkiluoto

Studies of Quaternary Deposits in Investigation Trench OL-TK17 on the Olkiluoto Study Site, Eurajoki, SW Finland (pdf) (2.4 MB)