Keywords
shear fractures
microstructures
SEM
rheology
How to Cite
Abstract
The qualitative and quantitative characteristics of microstructures in a till were analysed with SEM; it was also investigated whether the results depend on the till’s mesostructural characteristics. The till, exposed in a few open-cast browncoal mines near Konin in central Poland, is cut by numerous fractures which correspond to Riedel shear patterns, P-type structures and C-S type foliations. The fractures developed as a result of simple shearing induced by movementof the base of the Odranian ice sheet. On the basis of fracture density, two till types are distinguished: coarsely-brecciated till (wide spacing of fractures) and finely-brecciated till (closely spaced fractures). It is found that the fracture density is reflected in the microstructure of the till. The finely-brecciated till is characterised by a high porosity and has predominantly anisometric and fissure-like pores that also show a more clearly preferred orientation than the pores in the coarsely-brecciated till. In contrast, the coarsely-brecciated till has anisometric pores that show a less preferential orientation. The porosity of the coarsely-brecciated till is lower than in the finely-brecciated till. The finely-brecciated till probably represents a strongly deformed deposit, related in some cases to zones developed along thrusts that cut the till. Positive correlation between the porosity, the spatial arrangement of pores, and the density of fractures suggests a synsedimentary origin of the shear strain. This strain was accommodated by a particulate flow developed within both wide, pervasive zones and narrow, localised zones. The hydraulic conditions within the subglacial shear zone controlled rheological differences within the till during deformation and thus influenced the degree of the microstructure alteration.
References
Antonellini, M., Aydin, A. & Pollard, D.D., 1994. Microstructure of deformation bands in porous sandstones at Arches National Park. Journal of Structural Geology 16, 941-959.
Arch, J. & Maltman A.J., 1990. Anisotropic permeability and tortuosity in deformed wet sediments. Journal of Geophysical Research 95, 9035-9046.
Arch, J., Maltman, A.J. & Knipe R.J., 1988. Shear-zone geometries in experimentally deformed clays: the influence of water content, strain rate and primary fabric. Journal of Structural Geology 10, 91-99.
Bennett, R.H., Bryant, W.T. & Hulbert, M.H. (Eds), 1991. Microstructure of fine-grained sediments. Springer-Verlag, New York, 582 pp.
Bolton, A.J., Maltman, A.J. & Clennell, M.B., 1998. The importance of overpressure timing and permeability evolution in fine-grained sediments undergoing shear. Journal of Structural Geology 20, 1013-1022.
Borradaile, G.J., 1981. Particulate flow of rock and the formation of cleavage. Tectonophysics 72, 305-321.
Caine, J.S., Evans, J.P. & Forster, C.B., 1996. Fault zone architecture and permeability structure. Geology 24, 1025-1028.
Collins, K. & McGown, A., 1974. The form and function of microfebric features in a variety of natural soils. Geotechnique 24, 223-254.
Grabowska-Olszewska, B., Osipov, V. & Sokolov V., 1984. Atlas of the microstructure of clay soils. Wydawnictwo Naukowe PWN, Warszawa, 414 pp.
Hart, J.K., 2006. An investigation of subglacial processes at the microscale from Briksdalsbreen, Norway. Sedimentology 53, 125-146.
Kaczyński, R. & Trzciński, J., 1992. The physical-mechanical and structural properties of boulder clays of the Vistula glaciation in the area of Poland. Geological Quarterly 36, 481-508.
Kilfeather, A.A. & Van der Meer, J.J.M., 2008. Pore size, shape and connectivity in tills and their relationship to deformation processes. Quaternary Science Reviews 27, 250-266.
Kusky, T.M. & Bradley, D.C., 1999. Kinematic analysis of melange fabric: examples and applications from the McHugh Complex, Kenai Peninsula, Alaska. Journal of Structural Geology 21, 1773-1796.
Lash, G., 1989. Documentation and significance of progressive microfabric changes in middle Ordovician trench mudstones. Geological Society of America Bulletin 101, 1268-1279.
Mahaney, W.C., Claridge, G. & Campbell, L., 1996. Microtextures on quartz grains in tills from Antarctica. Palaeogeography, Palaeoclimatology, Palaeoecology 121, 89-103.
Maltman, A.J., 1987. Shear zones in argillaceous sediments - An experimental study. [In:] Jones, M.E. & Preston, R.M.F. (Eds): Deformation of sediments and sedimentary rocks.Special Publications Geological Society London 29, 77-87.
Maltman, A.J. (Ed.), 1994. The geological deformation of sediments. Chapman and Hall, 362 pp.
Menzies, J., Van der Meer, J.J.M. & Rose, J., 2006. Till as a glacial "tectomict", its internal architecture and the development of a "typing" method for till differentiation. Geomorphology 75, 172-200.
Murray, T. & Dowdeswell, J.A., 1992. Water througflow and the physical effects of deformation on sedimentary glacier beds. Journal of Geophysical Research 97 (B6), 8993-9002.
Raymond, L.A., 1984. Classification of melanges. [In:] Raymond, L.A. (Ed.): Melanges: their nature, origin and significance. Geological Society of America Special Paper 198, 7-20.
Rose, K.C. & Hart, J.K., 2007. Subglacial comminution in the deforming bed: Inferences from SEM analysis. Sedimentary Geology 203, 87-97.
Ruszczyńska-Szenajch, H., Trzciński, J. & Jarosińska, U., 2003. Lodgement till deposition and deformation investigated by macroscopic observation, thin-section analysis and electron microscope study at site Dębe, central Poland. Boreas 32, 399-415.
Ruszczyńska-Szenajch, H. & Trzciński, J., 2009. Soft lodgement till deposition and syndepositional deformation, Anielinek, the Polish Lowlands. Canadian Journal of Earth Science 46, 67-82.
Stankowski, W. & Krzyszkowski, D., 1991. Stratygrafia czwartorzędu okolic Konina [The Quaternary stratigraphy of the Konin area]. [In:] Stankowski, W. (Ed.): Przemiany środowiska geograficznego obszaru Konin-Turek. Wydawnictwo Naukowe UAM, Poznań, 11-31.
Statistica for Windows, 1998. Statsoft Inc., Tulsa.
Trzciński J., 1998. Ilościowa analiza mikrostrukturalna w skaningowym mikroskopie elektronowym (SEM) gruntów poddanych oddziaływaniu wody [Quantitative microstructural SEM analysis of soils influenced by pore water]. [In:] Grabowska-Olszewska, B. (Ed.): Geologia stosowana. Właściwości gruntów nienasyconych. Wydawnictwo Naukowe PWN, Warszawa, 113-150.
Trzciński, J., 2003. Mikrostruktury glin lodowcowych badane w skaningowym mikroskopie elektronowym [Scanning electron microscope analysis of microstructure in tills]. [In:] Harasimiuk, M. & Terpiłowski, S. (Eds): Sedimentological analyses of glaciogenic deposits. UMCS Press, Lublin, 63-77.
Trzciński, J., 2008. Microstructure and physico-mechanical properties of tills in Poland. Geologija 50, 26-39.
Trzciński, J. & Kaczyński, R., 1999. Microstructural nonhomogeneity of glacial tills. Visnyk Lviv. Univ. Ser. Mech. Match. 55, 152-157.
Vannucchi, P., Maltman, A., Bettelli, G. & Clennell, B., 2003. On the nature of scaly fabric and scaly clay. Journal of Structural Geology 25, 673-688.
Widera, M., 1998. Ewolucja paleomorfologiczna i paleotektoniczna elewacji konińskiej [Paleomorphological and paleotectonical evolution of the Konin Elevation]. Geologos 3, 55-102.
Włodarski, W., 2000. Litologia, stratygrafia i glacitektonika dolnego i środkowego czwartorzędu [Lithology, stratigraphy and glaciotectonics]. [In:] Skoczylas, J. & Biernacka, J. (Eds): Geologia i ochrona środowiska Wielkopolski. Przewodnik LXXI Zjazdu PTG. Bogucki Wydawnictwo Naukowe, Poznań, 112112-121.
Włodarski, W., 2009. Analiza strukturalno-kinematyczna kompleksu deformacji glacitektonicznych w strefie rowu Kleczewa (elewacja konińska, wschodnia Wielkopolska) [Structural and kinematic analysis of glaciotectonic deformation complex within Kleczew Graben zone (Konin Elevation, Central Polish Lowland)]. Prace Państwowego Instytutu Geologicznego 194, 75-100.
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