The origin of the silt size quartz grains and minerals in loess

Abstract

Abstract A permanent problem of the theories of loess formation is the origin of quartz grains of 20–50 μm size. This makes up the bulk of loess material. A fundamental question for more than 100 years has been how the huge amounts of silt size grains were produced. According to different explanations the coarse silt fraction could be produced by mechanical weathering caused by frost action, insolation, glacial grinding, particles originating from till and outwash plains and finally from fine-textured fluvial and lacustrine deposits (molasse) or commonly from sandy desert. Several kinds of processes can produce the initial material of loess according to Berg (1964) and Pecsi (1965) . Primarily, in the course of loess formation, pedogenic–geochemical processes had produced the coarse silt grain size. The unique loess fabric is a textured loam, not merely a simple sediment. Recently, Nemecz and Hartyani (1995) have collected samples in 10 μm steps of soil (and loess) for a subsequent analysis. Loess–paleosol samples were separated into 8–9 grain size fractions. The mineralogical composition of fractions were determined quantitatively and plotted in three dimensions. On typical granulometry diagrams for a Hungarian loess–paleosol series, two maxima can be recognized: one at