ISSUES IN PEDOSTRATIGRAPHY - SUPPORT FOR GEOSOL

Posted by Roger Morrison 15 Jun 1999 14:43:33

June 6 1999
ROGER B. MORRISON, Ph D
Former senior research geologist (retired), U. S. Geological Survey
Chair, Working Group on Pedostratigraphy, Commission on Paleopedology,
INQUA
13150 West Ninth Avenue., Golden, Colorado, U.S.A.
Voice: 303-233-1997. Fax: 303-233-0495. E-mail:
rbmorrison@earthlink.net
WELCOME AND PREAMBLE
This is my first e-mail on pedostratigraphic issues, directed chiefly
(but by no means exclusively) to members of the INQUA Commission on
Paleopedology, prior to and anticipating in-depth discussion of topics
at the INQUA XV Congress this summer at Durban, South Africa. First,
something about my own background in pedostratigraphy.
I was fortunate in getting my early experience near the inception of
interest in pedostratigraphy by working for the U. S. Geological Survey
on the two chief pluvial-lake sequences in the Great Basin of the U.S.,
those of Lakes Lahontan and Bonneville (Morrison, 1964a, 1965; 1991).
Both lakes had huge drainage areas and their terminal basins contain
superb, very detailed sedimentary and pedologic-climastratigraphic
records. These records are far more detailed and complete than those
available from any glacial and alluvial sequences, equivalent in detail
and complementing the loess records of eastern Europe and China. I
became intrigued with the many paleosols intercalated with the
lacustrine, eolian, and alluvial sediments, first for the information
they gave on various lake recessions, then for what they can yield on
climate and vegetation while they formed. Later my interest in
paleosols broadened both geographically and topically. I attended many
field excursions focused on soil science and Quaternary geology in the
U.S. and Europe, and conferred with soil-scientists and
pedostratigraphers such as Hans Jenny, Guy Smith, Pete Birkeland, Julius
Fink, John Frye, Karl Brunnacker, Wolfgang Schirmer, Lee Gile, George
Kukla, Vojen Lozek, Leon Follmer, and many others.

Some of my conclusions after several decades of pedostratigraphic
research are:

1. Paleosols commonly are among the best records of metastability
episodes in landscape history, when little or no erosion or sediment
deposition took place at a given site; conse-quently, paleosols are
important parts of the stratigraphic record.

2. As significant elements of the stratigraphic record, paleosols
deserve to be classified and treated rigorously as stratigraphic units.
This is why I (1964b) coined and defined GEOSOL as the term for the
basic pedostratigraphic unit. It was adopted in this sense in the North
American Stratigraphic Code (1983).

3. The physical and biologic records indicate that paleosols formed over
distinct, com-monly widely separated episodes of time in response to
infrequent combinations of climatic factors that induced both
land-surface stability (minimal erosion and deposition) and a more
accelerated rate of bio-physiochemical weathering than before, lasting
long enough to develop a distinct soil profile. Higher-than-before
temperature increases appear to be associated with the intermittent
stronger soil-forming episodes, not just precipitation increases. This
is why paleosols throught the world correlate nicely with Quaternary
interglacials and interstadials-and therefore can be used as
stratigraphic datums..

This brings us to the question of THRESHOLDS in
temperature-precipitation conditions that, if crossed, trigger certain
kinds of soil-profile development. This subject remains nearly
unexplored. What were the climatic, time, and other thresholds that
induce a Frost Gley versus a Podzol/Spodosol, a Parabraunerde/Udalf, a
Haplargid, an Argiustoll, or a Udult? Our knowledge about the past
climatic episodes that produced such different soils remains primitive.

OUR GOAL SHOULD BE TO GET A PEDOSTRATIGRAPHIC CLASSIFICATION INCLUDED IN
THE INTERNATIONAL STRATIGRAPHIC GUIDE
A pedostratigraphic classification is not yet included in the
International Stratigraphic Guide, which follows the 1983 North American
Stratigraphic Code in many other respects. The International
Stratigraphic Guide (1994, p. 2) states: "Soils and soil-strati-graphic
units have not been covered in this second edition of the Guide. The
stratigraphic treatment of soils needs additional consideration before
attempting to formalize principles and procedures and to incorporate
soil-stratigraphic units into the Guide. These units may be the subject
of future discussion by the ISSC."

The INQUA Paleopedology Commission should begin formal in-depth
discussions with key members of the INQUA's Stratigraphic Commision and
the International Stratigraphic Commission, with the goal of getting
pedostratigraphic units included in the International Stratigraphic
Guide.

CONCLUSION
A pedostratigraphic classification remains (barely) in the current
North American Stratigraphic Code, with GEOSOL as its fundamental and
sole unit. The term GEOSOL is becoming used widely among U. S.
Quaternary geologists and geomorphologists.

Some workers, including myself, recognize that improvements should be
made in the definition of GEOSOL in the NASC; also, the code should
admit subdivisions of a GEOSOL, akin to members of a Formation and the
divisions of pedogenic Paketts in the loess sequences of central
Europe. Also, provision should be made for recognition of pedologic
changes (pedofacies, similar to chronocatenas) within the same
pedostratigraphic unit.

Despite any perceived imperfections in the definition of GEOSOL (which
can be corrected later), I urge all members of the INQUA Paleopedology
Commission to join together in supporting the North American
Stratigraphic Code in (1) recognizing a pedostratigraphic
classification, and (2) adopting GEOSOL as the basic pedostratigraphic
unit.

As I have explained, the whole status of recognition into a formal
stratigraphic code of a pedostratigraphic classification and
pedostratigrapic units is very tenuous among the geologic profession,
including many notable stratigraphers. Let us not splinter ourselves
with arguments such as whether GEOSOL is the best name for the basic
pedostratigraphic unit or (until later) how it should be defined
pedologically in the Code. Only after considerable difficulty was the
pedostratigraphic classification admitted into and retained in the North
American Stratigraphic Code and GEOSOL accredited as its basic and sole
unit. Let's move on to more important matters, such as getting
appropriate subdivisions of GEOSOLS (pedomembers) and their lateral
variants (pedofacies) admitted into the North American Stratigraphic
Code---and pedostratigraphic units included in the International
Stratigraphic Guide.

REFERENCES
American Commission on Stratigraphic Nomenclature, 1961, Code of
stratigraphic nomenclature: Amer. Assoc. Petroleum Geologists Bull.,
v. 45, P. 645-665.

International Subcommission on Stratigraphic Classification,
International Union of Geological Sciences, International Commission on
Stratigraphy, 1994, International Stratigraphic Guide, a guide to
stratigraphic classification, terminology, and procedure, 2d ed.:
Boulder, Colorado, Geological Societry of America, 214 p.

Morrison, R. B., 1964a, Lake Lahontan, Geology of the southern Carson
Desert, Nevada: U.S.Geological Survey Professional Paper 401, 156 p.

Morrison, R. B., 1964b, Soil stratigraphy: Principles, applications to
differentiation and correlation of Quaternary deposits and landforms,
and applications to soil science: University of Nevada, Reno, Ph D
Dissertation: Dissertation Abstracts, v. 28, no. 4, 1967.

Morrison, R. B., 1965, Lake Bonneville, Quaternary stratigraphy of
eastern Jordan Val-ley south of Salt Lake City, Utah: U. S. Geological
Survey Professional Paper 477, 80 p.

Morrison, R. B., 1978, Quaternary soil stratigraphy-concepts, methods,
and problems, p. 77-108 in Mahaney, R., ed., Quaternary Soils: Norwich,
England, GeoAbstracts.

Morrison, R. B., 1991, Quaternary stratigraphic, hydrologic, and
climatic history of the Great Basin, with emphasis on Lakes Lahontan,
Bonneville, and Tecopa , Chapter 10 in Morrison, R.B., ed., Quaternary
nonglacial geology; conterminous U. S.: Boulder, Colorado, Geological
Society of America, The Geology of North America series, v. K-2, p.
353-371.

North American Commission on Stratigraphic Nomenclature, 1983, North
American Stratigraphic Code: American Association of Petroleum
Geologists Bull. v. 67, No. 5 (May), p. 841-875.