INQUA/ISSS PALEOPEDOLOGY COMMISSION NEWSLETTER

Open Letter on Pedostratigraphic Issues

Roger B. Morrison, 13150 W. 9th Ave., Golden, CO 80401

Editor's note. [The following Open Letter by R. B. Morrison, Chair, Working Group on Pedostratigraphy reports on the discussions during the 1993 PP Symposium and goes beyond to seek response from WG members and PP Commission members. His objective is to encourage further discussion on the principles, nomenclature, techniques and issues of pedostratigraphy. For further information refer to the following paper, "How can the treatment of pedostratigraphic units in the North American Stratigraphic Code be improved?" This is a revised version of his paper that first appeared in the preprint designated as NL10-Part D.]

Issues discussed in sessions of the Working Group on Pedostratigraphy:

During the two sessions of the working group (attended by delegates from China, Australia, New Zealand, Poland, Russia, U.S., Israel, and Germany), chiefly nomenclatural/definition topics were discussed, as they relate to the current North American Stratigraphic Code and to usage in other areas. Two controversial issues were put to vote:

1. The North American Stratigraphic Code adopted Geosol as the term for the fundamental formal pedostratigraphic unit. Is this acceptable for use in your country? (This question received a nearly unanimous yes vote.)
2. Is "relict paleosol" an appropriate term for surface paleosols? (These are paleosols on old geomorphic features, such as river terraces, alluvial fans, and glacial moraines, that have remained exposed at the land surface since the feature was formed. "Relict paleosol" has been widely used in the U.S. for more than 50 years.) This question received a nearly unanimous no vote. This raises the question of whether there is a term preferable to "surface paleosol."

Relevant issues discussed during general meetings of the Symposium:

The same question, "Is relict paleosol an appropriate term for surface paleosol?" was put to vote. The vote again was overwhelmingly against equivalency. The objections were about choice of words; no concensus was reached.

Another question was put to vote: Is series or soil series a desirable name to designate lateral changes in character of a pedostratigraphic unit (paleosol, Geosol, perhaps chronocatena if it becomes accepted as a pedostratigraphic designation)? After considerable discussion, the general vote on this question was almost unanimously NO. Commentary: Reasons for the negative vote: The term (soil) series is used in the U.S. as the basic soil-classification unit for soil mapping. However, soil-series units invariably lack true stratigraphic definition in geologic terms. Moreover, series is preempted as a stratigraphic term because it is used in both the North American (1983) and International Stratigraphic Codes (1994) to designate formally those units in conventional chronostratigraphic classifications that rank above a stage and below a system.

Topics that the Working Group on Pedostratigraphy might explore:

1. Ways in which general understanding of the principles and techniques of pedostratigraphy can be enhanced among pedologists and Quaternary geologists. In my experience, studies of purely surface (relict) paleosols on old landforms (river terraces, alluvial fans, etc.) commonly are emphasized to the detriment of true in-depth pedostratigraphic studies. Surface paleosols typically are polygenetic and provide only fragmentary highly compressed and overprinted information on the very complicated history of Quaternary climatic, biotic and other changes. Their physical and chemical characteristics record chiefly extreme events, such as effects of interglacial/interstadial warm episodes, and in places, frost action during glacials. Their chronologic information, particularly on details of sequential events, is very limited and also controversial due to reworking/replacement of older material by younger. Therefore, studies of surface paleosols alone are of limited value; they attain greatest value if they are integrated with pedostratigraphic studies of the most complete depositional sequences in a given region.
2. How to overcome the conceptual/semantic problems that exist between geologists and soil scientists, who typically receive different training and "don't speak the same language?"
3. If relict paleosol is rejected as a name for a surface paleosol, is there a better name?
4. Is pedofacies an appropriate term for designating lateral changes in character of a given aleosol/Geosol?
5. Do chronocatenas warrant recognition as stratigraphic units? (Other types of catenas may include paleosols of diverse ages and stratigraphic context, and therefore cannot be pedostratigraphic units.) Are the terms chronocatena and paleosol comparable and perhaps interchangeable, where both presumably have the same stratigraphic position and represent the same time interval?

Issues for debate:

1. The International Stratigraphic Code does not recognize a pedostratigraphic category of stratigraphic units. Should the INQUA Paleopedology Commission strive for such recognition?
2. The North American Stratigraphic Code (NASC) includes a pedostratigraphic category, with Geosol as the fundamental unit. Is this Code's definition of Geosol adequate? If not, how should it be improved?
3. Is the current NASC's explication and formal designation of composite (amalgamated or welded) paleosols adequate? If not, how should it be amended?
4. Do pedocomplexes deserve formal recognition, and under what criteria? The current NASC does not recognize pedocomplexes as such. These are multistory close-together sequences of paleosols. They comprise so many closely spaced paleosols that they are integral to the lithologic character of the unit; therefore, they can be treated either as lithostratigraphic or pedostratigraphic units.
5. Should pedofacies receive/require formal recognition? The NASC states that a paleosol may have "a range of physical and chemical properties in the type area, rather than 'typical' properties exhibited in a type section. Consequently, a pedostratigraphic unit is characterized on the basis of a composite stratotype." It seems that the NASC hints at the existence of pedofacies without labeling them as such and without providing for formal designation of individual facies (akin to designation of lithofacies in a lithostratigraphic unit).
6. What sort of minimal pedologic characteristics should be established for paleosols that are proposed to be formally named (i.e., to be designated a Geosol)? How about maximal constraints?—e.g., for deep profiles of tropical paleosols, or for amalgamated paleosols that represent very long time intervals, such as the Yarmouth-Sangamon paleosol of Iowa?
7. What recommendations can the Paleopedology Commission make to the North American Stratigraphic Commission and the International Stratigraphic Commission and the International Stratigraphic Commission?

Editor's Note. The conclusion of this Open Letter is an appeal for readers to respond to important issues concerning how terminology can best serve pedological and geological perspectives. Terminology that is illogically restricted or overextended causes misunderstandings; terms that have multiple meanings and applications, such as "soil," cause confusion. A worthy goal for our Commission is to select a set of terms with appropriate explanations that all can use. So ask yourself, what terms do I need and what terms do others need? Can we compile a glossary to serve as a reference point for all earth sciences? Send your response to Roger or a Commission officer near you.