SOILS, PALEOSOLS, AND GEOSOLS: A Commentary

Posted by Vance T. Holliday 15 Jun 1999 13:47:47

Department of Geography, 550 N. Park St., University of Wisconsin, Madison, WI 53706-1491, USA

I am writing to offer my views on the soil terminology proposed by the Working Group on Definitions used in Paleopedology(PP Newsletter
#14). I realize that these comments come after several drafts by the WG, but publication in PP #14 was the first time I saw them. I want to present
some alternative views on the terms soil, paleosol, and geosol for consideration among the community of soil-geomorphologists,
soil-stratigraphers, and paleopedologists.

The new definition of paleosol is an attempt to provide a practical, unambiguous definition for a term that historically has been quite
ambiguous. The proposed definition for paleosol does not resolve the issue, however. The new definition eliminates ambiguities, but
establishes the somewhat arbitrary criteria of pedogenesis in the Pleistocene or earlier geologic periods. This creates a situation similar to that
for classification in the U.S. Soil Taxonomy: considerable information must be assembled before the term can be applied. In the case of the new
definition of paleosol, data on the age of the soil and its genetic evolution must be available before a field scientist can know whether to
properly call the zone in question a soil, a paleosol, or a buried soil. This seems illogical and is clearly impractical for field workers. These sorts
of data are not always easy to come by and genetic interpretations can remain contentious.

I have never understood why the term paleosol is so widely used in Quaternary geosciences. I see no practical reason why the terms soil and
buried soil can not be applied to most Quaternary soils. Certainly the term soil has been applied in many different ways and has many
definitions, but for soil-geomorphologists, soil-stratigraphers, and paleopedologists, the meaning of the term is clear. In over 20 years of field
experience and research, I've never encountered any confusion in the use of the term soil in discussions or communications with colleagues
and students. Moreover, I've seldom used the term paleosol, and have not been hindered in my work. The necessity of maintaining the term
paleosol eludes me, though I realize that it is here to stay. What is needed is a clear, simple, easy-to-apply definition that does not require
chronometric or other analytical data before the appropriate term can be decided upon.

I propose that paleosol be applied to soils that are lithified. In geology, a sand is a sand, for example, regardless of age or stratigraphic position.
We do not call a Pleistocene or older sand or a sand associated with a past landscape a "paleosand." If a sand is lithified, however, we call the
deposit a sandstone. Why can't this same, common sense approach be applied to soils? i.e., define a paleosol as any soil that is lithified.
Although there may be debate over what constitutes lithification, few Quaternary soils will be involved. The concept is generally easy to apply
in the field upon visual examination, and requires no

data on numerical age control. Soiland buried soil can be applied to soils that are not paleosols.

The adoption of the term geosol by the WG as well as in the North American Stratigraphic Code (1983) also is unfortunate. From the time it was
proposed (by Morrison in 1967) until its adoption in the Code in 1983, it was seldom applied, clearly indicating that it lacked real utility or that it
was not in fact superior to soil as a formal pedostratigraphic term. The term geosolhas not been shown to clarify any soil-stratigraphic issues.
Again, the term soil seems quite adequate as a formal soil-stratigraphic term.