Aluskorra murenemiskooriku koostis ja geotehnilised omaduste Vihterpalu F332 puuraugus [Bakalaureusetöö. Juhendaja: R. Hints]

The thesis addresses geochemical and geotechnical properties of the Neoproterozoic paleoweathering crust of the Estonian crystalline basement from the Vihterpalu F332 drill core. Interest towards a better characterization of such complexes has lately increased due to several perspective deep-infrastructure projects. The paleo-weathering crust of the crystalline basement in the Vihterpalu area lies in approximately depth 200 m and is covered by Phanerozoic sedimentary rocks. The paleo-weathering crust there has evolved on Si-poor magnetite-rich amphibolites.

For the study, 23 samples were collected from the paleo-weathering profile. All samples were analysed using X-ray diffraction and X-ray fluorescence techniques to characterize chemical and mineralogical variations in the weathering profile. Additionally, eight selected samples were used for geotechnical tests to determine parameters such as point load index, grain density, porosity, and also for microscopic studies.

Based on the results, the weathering crust was divided into three sections: paleosol (1.0 m), saprolite (4.0 m), and saprock (29.0 m). The uppermost red clay-rich paleosol horizon is highly weathered residual complex with CIW and CIA index > 90. Its mineral assemblage is composed of kaolinite, hematite, illite-smectite, and illite. Greenish saprolite horizon with secondary mineral complexes and signs of pervasive geochemical alteration showed complex Fe-Mg-rich clay mineral assemblage with celadonite. The study is the first to report on a finding of celadonite (glauconite) in the paleo-weathering crust of Estonia. Isochemical weathering processes prevailed in the saprock part of the weathering profile. The studied paleo-weathering crust has also undergone diageneticmetasomatic K-alteration during post-weathering evolution.

The mechanically weak part of the paleo-weathering crust in the Vihterpalu drill core includes paleosol, saprolite and upper saprock. The most significant weakening of the rock is related to the development of micro-fissures and loss of structural integrity during the primary stages of weathering.