The Development of Frost‐weathering Microstructures on Sand‐sized Quartz Grains: Examples from Poland and Mongolia

Abstract

ABSTRACTQuartz grains, 0.25−1.0 mm in diameter, taken from Pleistocene sands and a palaeo‐active layer in Poland (Łódź Teofilów) and from silty‐clayey sediments of the contemporary active layer near Ulaanbaatar (Mongolia) were analysed using a scanning electron microscope (SEM). Other analyses included granulometric composition, and frosting and rounding of quartz grains. The effects of frost weathering comprise several microstructures, such as breakage blocks (>10 µm and <10 µm), surface coating and scaling, among which breakage blocks <10 µm are apparently the most common. Two types of frost weathering were distinguished. Weathering of the P type is mainly initiated on convex fragments of grains as the result of ice segregation. Weathering of the F type is linked to the volumetric expansion of ice and usually observed within concave linear microstructures. A frost action index (FAI) was developed based on the frequency of occurrence of microstructures from frost weathering. The FAI value varies between 0 and 3, and the higher the value, the more intensive the frost weathering. The value of the FAI in sediments from the Polish study site is relatively low with a maximum barely exceeding 1. The FAI values from the Ulaanbaatar site are higher in all of the sediment samples with a maximum of 2. Copyright © 2011 John Wiley & Sons, Ltd.