Soils & the Stratigraphic Code

Posted by Keith Crook 18 Jun 1999 06:18:53

G'day Everyone: I've been following with considerable interest,
interspersed with occasional bouts of "deja vu", the email "blizzard"
generated by Roger Morrison's initiative.

After checking with Australian-based colleagues on current and recent
practice, my request to the INQUA Paleopedology Commission is, for the
immediate future: Please move slowly, and take no final decisions. The
rationale for this request is set out below. Before I come to that,
however, I'd like you to know something of my background, as it bears on
assessment of the relevance of the points I wish to make.

I am a geoscientist trained (at Sydney University, Australia) in both
geology and soil science. During the past 45 years I have taught and
supervised research theses in both fields in geology departments,
principally at ANU, in part in association with soil scientists and
physical geographers. My own research fields are in ancient & modern
clastic sedimentology (particularly alluvial and deep water marine
sediments), tectonics, marine geology and surficial geology. In the 1960's
I was an active member of the Australian Committee for Stratigraphic
Nomenclature.

In 1971 I co-authored (with Roy Brewer, a soil scientist, & Gary Speight, a
geomorphologist) a proposal (J.Geol.Soc.Australia, 17, 103-114) to
incorporate into the Australian Code of Stratigraphic Nomenclature the
category "Pedoderm", preceded by a geographic name, as the fundamental
mappable unit mantle of soil (a soil stratigraphic unit), with provision
for named constituent horizions such as "Laterite, Silcrete, Kunkar,
Calcrete, or Bole". This was not formally adopted, but became the subject
of a recommendatory footnote in the last published edition of the code in
1973 (JGSA 20, 111). Soon after, I think, Australia resolved to adopt the
International Code of Stratigraphic Nomenclature.

This week, Cathy Brown of AGSO checked the Australian Stratigraphic Index
for me, and came up with a count of registered names containing the
following terms:

Pedoderm/pedoderm 18
Laterite/laterite 11
Silcrete/silcrete 16
Kunkar/kunkar 0
Calcrete/calcrete 11
Bole/bole 0
Ferricrete 4
Surface 34
Profile/profile 4
Geosol/geosol 0
Paleosol/paleosol 12
Soil 16 (no soil entries)

What this tells me is that soil scientists, paleopedologists and surficial
geologists in Australia have been able to work quite satisfactorily in many
cases without resorting to formal stratigraphic nomenclature, despite its
availability. This is a very significant conclusion, because paleosols
(complete or truncated) are VERY widespread in Australia. They occur in a
very wide range of settings: at the surface of landscapes where they are
relicts of past climates, many of them pre-Quaternary; buried (i.e. in a
stratigraphic context); and exhumed. (Here I am excluding paleosols that
occur in deformed and lithified rock sequences.)

This is not surprising in a continent that has experienced NO significant
orogeny since the Late Paleozoic, has very extensive planate surfaces
(highest point on the continent is <2500m), has internal drainage (to Lake
Eyre) for 1/3 of its area, and NO organised drainage for a further 1/3 of
its area, has a regolith >100m thick over wide areas which is known to
include components as old as 300Ma, and is probably older; and has lacked a
significant up-wind source of atmospheric dust since India's mid-Cretaceous
escape from Gondwanaland and perhaps earlier.

Consequently there has been a considerable interaction between soil
scientists, geomorphologists, Quaternary geoscientists, geologists and
geophysicists in Australia. One manifestation of this is the Cooperative
Research Centre for Landscape Evolution and Mineral Exploration (CRC-LEME):
. Its work, which is extensive, has apparently not
so far required formal stratigraphic nomenclature.

The Australian experience leads me to several conclusions:

1. Paleosols are as real as sandstones, and they are quite common in
ancient lithified stratigraphic sequences as well as in the landscape
contexts mentioned above. I'm not at all surprised that one of the leading
international workers on these ancient paleosols, G.J. Retallack, did his
initial university studies in Australia.

2. Paleosols, and their relevance to the International Stratigraphic Code,
cannot be cannot be confined to Quaternary examples. Whatever is proposed
for inclusion in the Code has to be GENERALLY applicable.

3. The Quaternary of glacial and periglacial areas in North America and
Europe, and the loess plateau of China does NOT provide a range of paleosol
contexts that is sufficiently comprehensive for global use. They are
adequate analogues for some situations in Australia, but many situations
there are very different in age, age-range, climate or geomorphic setting.
(This is also true, but in a very different way, for Hawai`i, where much of
the stratigraphy and many paleosols are volcanologically modulated. But
that's an additional, and largely separate, problem.)

4. As conceptual stratigraphic units, paleosols are analogous to (but
differ significantly from) lithostratigraphic units. They have no
INTRINSIC chronostratigraphic or paleoclimatic significance. Some
paleosols that are mappable over wide areas and occur in part in
stratigraphic sequences, such as the Sangamon Geosol, may be used as
pedo-chronostratigraphic units, and/or pedo-climatostratigraphic units, but
these are accidental additional attributes. They are welcome additions,
when so demonstrated, but cannot form the basis for a descriptive
stratigraphic nomenclature of paleosols.

5. I wish to add the following item to the list of required reading
generated by this email discussion. Its recommendations are a beginning
only. Much work remains to be done.

Brewer, R., Crook, K. A. W. and Speight, J. A., 1970. Proposal for soil
stratigraphic units in the Australian stratigraphic code. J. Geol. Soc.
Aust., 17, 103-111.


Aloha, Keith.

*******************************************
Keith A W Crook, Science Director,
Hawai'i Undersea Research Laboratory
University of Hawai'i 1000 Pope Rd MSB 303
Honolulu HI 96822 USA
Ph: +1-808-956-9429; Fax: +1-808-956-9772

www.soest.hawaii.edu/HURL/hurl.html
Office location: Marine Science Bldg 232
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[Visiting Professor, Earth Sciences]
[James Cook University, North Queensland]
[Townsville, QLD 4811 AUSTRALIA]
[Ph: +61-7-4781-4546; Fax: +61-7-4725-1501]
http://www.jcu.edu.au/school/earth/people/Crook.html
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