“In-situ” theories of loess formation and the significance of the calcium-carbonate content of loess

Abstract

It is generally accepted that loess deposits form by action and yet the concept of “loessification” is still encountered, particularly in some European literature. Loessification often seems to be invoked when the deposit being investigated is rich in calcium carbonate because the use of the concept depends upon an eclectic definition of loess. Loessification is irrelevant if loess is defined in terms of the fine quartz material, but may be meaninful if the loess is defined in terms of calcium carbonate. The Russell theory of in-situ formation can possibly be reconciled with deposition by eolian action and production of quartz material by glacial grinding but the Berg theory cannot, and appears to be based on false premises. The “soil science” approach to the problem of loess formation may be responsible for the overvaluing of the significance of the carbonate content; the “geological” approach, with some emphasis on transportation problems, leads logically to the concept of eolian deposition but has, so far, failed to focus attention on the problem of the formation of the actual loess material. The fine quartz material is mostly formed by glacial grinding; there appear to be no other natural forces powerful enough to produce appreciable quantities of loess-sized quartz particles. Deposition of the secondary carbonate is usually the last of the significant stages in the formation of the deposit; scanning-electron-microscope studies suggest that it exists as discrete encrustations (gnarls) rather than as continuous coatings on the quartz grains.