Arnt Bronger and John Catt
1. Overview of Objectives of the Commission on Paleopedology
Paleopedology is regarded as the study of paleosols, which have in turn been somewhat loosely defined as "soils formed on a landscape during the geologic past" (Ruhe 1956; Yaalon 1971). We distinguish a) buried paleosols (fossil soils) from b) non-buried paleosols (relict soils or relict paleosols), and c) exhumed paleosols (once buried and subsequently re-exposed by erosion). According to our membership in both scientific unions our studies on buried paleosols are more related to INQUA whereas our studies on non-buried paleosols are more related to IUSS (see Fig. 1).
a) One of the most important uses of buried Quaternary paleosols has been the paleoclimatic interpretation of the multiple soils in long loess sequences in various parts of Europe, Central Asia, China, USA and other regions. Examples have recently (1998) been published from North Italy (Busacca and Cremaschi), central USA (Markewich et al.) and East and Central Asia (Bronger et al.) in special paleopedological issues of Quaternary International and Catena (see below). These loess-paleosol sequences have provided detailed records of climatic change for the last 2.6 million years, which are potentially at least as detailed as the oxygen isotope record obtained from deep oceanic cores. Like the oceanic cores, they also show a good relationship to the variations of solar radiation resulting from perturbations of the earth's orbit, the so-called Milankovitch curves. Paleosols have undoubted importance for understanding the processes driving natural climatic change, not just in the Quaternary (glacials, interglacials, interstadials) but throughout geological time, because the Milankovitch curves have now been identified in cyclic sediment sequences of many pre-Quaternary periods. The same processes will undoubtedly control future climatic change, though the more immediate effects of atmospheric pollutants (greenhouse gases) may be superimposed on those related to the Milankovitch curves.
The main advantage of the loess-paleosol sequences in
reconstructing past global climate change is that they cover all or much
of the Quaternary period in many different geographical regions. When the
paleosols are adequately dated and sufficiently interpreted, they will
allow geographical variation of past climates to be assessed more reliably
and in more detail than is possible by any other method known at present.
This is one of the tasks of the Commission on Paleopedology of INQUA (Fig.
From: Bronger & Catt, 1998
b) Paleopedology is also important for a proper understanding of the agrochemical and agroenvironmental behaviour of surface (non-buried) paleosols, and it plays a vital role in the multidisciplinary pedological study of soils. We therefore see paleopedology as occupying an important position in soil science (Fig. 1) with considerable potential for a major co-ordinating role through a genetic system of soil classification (Bronger & Catt 1998). This is the main task of paleopedology in the IUSS especially in Commission V, where we have the status only of a Working Group (see Report of the business meeting in Berlin in NL-12 and below).
For these areas of responsibility we need first to solve the problerns of defining paleosols. Considerable progress was made at the Inter-Congress Symposium in Champaign, IL, USA 1993 especially by the Working Group "Definitions, used in Paleopedology (Paleopedology Glossary)" run by J.A.Catt. First results are summarized in Newsletter (NL) 11/2, 35-37 Oct.1995) and in Quat. Int. Vol.51/52, p.85 (1998), a revised version is published in our Newsletter (NL) 14 (1997, p.13-14). Some problems may be emphasized briefly (see also Bronger and Catt, 1998):
1. There is a considerable measure of agreement over what is meant by a buried paleosol. It is a soil buried by younger sediment sufficiently thick that any subsequent pedogenesis has not affected its entire thickness and therefore has not influenced the buried soil. Problems start, however, with postpedogenic (or diagenetic) changes after burial. A frequent example is the recalcification of (almost) all paleosols buried by loess deposition. These causes severe problems for paleosol classification if property based systems are recommended (see below) although soil micromorphology can distinguish between primary and secondary calcites. Another difficulty is caused by the fact that most buried paleosols in loess sequences are more or less truncated, so it is difficult e.g. to separate Mollisols (Phaeozems, Chernozems, Kastanozems) from Luvisols. Because of the rapid decrease of humus content even in buried Holocene Chernozems, e.g. in the Central Loess Plateau of China (Bronger and Heinkele 1989), it may be even difficult to distinguish them from Kastanozems using the criterion of colour, as in the FAO-UNESCO system.
2. Non-buried paleosols (relict soils) do not suffer from these difficulties but there are even more problems of defining and recognizing them. A non-buried paleosol shows two or more sets of properties which can be related to different combinations of soil-forming factors (especially different climates and vegetation) through sets of often incompatible soil forming processes. Incompatibility of processes implies two or more environmentally different periods of soil development.
Non-buried paleosols are also important for a full and correct understanding of landscape history, which is essential for a proper appreciation of many modern environmental problems. For example the soil cover of central and south India consists mainly of Vertisols ("Black soils") and Lixisols (Rhodustalfs or "Red soils") both of which are non-buried paleosols because they formed in an earlier period of much moister climate than the present. In the present distinctly seasonal semi-arid conditions (<1000 mm annual rainfall and very high potential evapotranspiration) earlier soil- forming processes such as deep weathering and strong kaolinite formation have almost ceased; instead secondary carbonate is accumulating in the saprolite (Cr) and lower parts of the Lixisol Bt horizons (Bronger and Bruhn, 1989), and under arable agriculture soil erosion is becoming a severe problem. It is widely accepted that soil erosion can be tolerated from a crop production viewpoint provided soil formation keeps pace with it to compensate for the losses. However, in today’s semiarid India the soil development processes have changed and the rate of compensatory regeneration of soil is in effect (almost) zero. The erosion there is consequently a permanent loss of the country's most important natural resources, but it has not been recognized as such because the soils were not identified as paleosols. The erosion now occurring in many other countries (Oldeman et al., 1990) is probably a similar irreplaceable loss of resources inherited from earlier geological periods. This example emphasizes the importance of paleopedology even for applied aspects in the Commission V of IUSS, because in the tropics and subtropics most soils are paleosols.
The delimitation of non-buried paleosols from so-called "modern" soils is still unsatisfactory. To stimulate further discussion the vetusol concept of M. Cremaschi (1987) may be re-introduced. A vetusol (vetus, Latin: old) is a non-buried soil "which underwent the same or very similar processes of soil formation over a generally long period of time, including at least some part of the Pleistocene" (op. cit., 234). With this suggestion we are back to the question of climatic changes of the Quaternary in different regions.
For our paleopedological approach the concept of a pedostratigraphic unit introduced by R.B. Morrison, chairperson of the WG "Pedostratigraphy", should be a real challenge for the Paleopedology Commission. His valuable ideas are recently summarized in Quat. Int., Vols. 51/52 (1998), p.30-33, 81-82 and are an important contribution towards a (trans) continental pedostratigraphy which the Paleopedology Commission should develop. The "fundamental and only unit in pedostratigraphic classification is a geosol” comprises one or more differentiated pedologic horizons. A geosol “has a consistent stratigraphic position and is defined at a type locality where the horizons are buried by younger deposits.... In the North American Stratigraphic Code (NASC), article 57a states a composite geosol can still be regarded as a pedostratigraphic unit. It is a polygenetic paleosol, recording more than one soil-forming episode (R.B.Morrison); it is also termed "welded paleosol" after Ruhe and Olson (1980; see Olson and Nettleton, 1998). R.B.Morrison names as an example the "Yarmouth-Sangamon paleosol which represents about 700 000 yr in Iowa". However, up to a dozen paleosols, partly as pedocomplexes (see below) and more or less separated by loess, can be found in this time interval in long loess sequences (up to 65 m) in China or Tadjikistan (Bronger et al. 1998). Therefore the idea of R.B. Morrison that stratigraphic codes such as that of the NASC "should recognise pedostratigraphic ranks subordinate to geosol" which he termed "pedomembers" (op.cit. p.31) should be supported.
Morrison also distinguishes compounded (multistory) paleosols defined as "two or more paleosols separated by small thickness of not soil-sediment (C horizon)..." (p.31). These compounded paleosols (compounded geosols?) are described as pedocomplexes, which is the name for a fundamental pedostratigraphic unit in Central Europe, used for decades in many publications. Morrison continues with compounded paleosols if "traced laterally, these pedocomplexes commonly merge into a single composite paleosol". The necessity to distinguish between composite and compounded paleosol (geosol) might be questioned; the composite geosol is also "multistory" or polygenetic.
The concept of pedostratigraphic unit was a major point of discussion in Poster Session P 25 of the PP - Commission (Convenor: J. A. Catt) in Durban. J.A. Catt (see below) summarizes the discussion about the paleopedology glossary in the report of the PP Commission workshop on definitions.
Finally Morrison proposed litho-pedostratigraphic complexes "that exist throughout the world. These comprise stacks of numerous paleosols ... closely spaced ..." (p.31). His conclusion that "the individual paleosols cannot be reliably differentiated and traced very far; the whole complex is best treated and mapped as lithostratigraphic unit" (p.31) may be valid but only in certain areas. Their existence as world-wide litho-pedostratigraphic complexes shows that in other areas, e.g. in Central Asia and China (see above), the equivalent units can record the most detailed paleoenvironmental history (e.g. Bronger et al. 1998, p.l-17).
Even more discussion is needed for the classification of paleosols. Two proposals were presented in Champaign in 1993; they are now published together with several other papers presented at the 1993 Inter-Congress Symposium in Vols. 51/52 of Quaternary International, 1998. Both proposals are based on properties.
The proposal from P. Buurman is based mainly on the FAO-UNESCO soil classification system, whereas that of the WG on "Classification of Paleosols" chaired by W.D. Nettleton recommended the U.S. Soil Taxonomy as a basis. Both international classification systems do not distinguish, however, between a soil in situ and a soil sediment (redeposited soil material) which is essential for stratigraphic, geomorphological and paleoenvironmental interpretation. Also they do not distinguish between profiles which have been truncated by erosion or contain discontinuities resulting from erosion followed by redeposition and renewed pedogenesis. Soil Taxonomy uses present climatic factors at high taxonomic level, which leads to confusion over the recognition and paleoclimatic interpretation of relict features, formed in past periods of different climate.
The literature cited in this chapter could be found in the special paleopedological issues of Quaternary International Vols. 51/52, 1998, 221 pp. and CATENA, Vol. 34, Nos. 1-2, 207 pp. (see below).
To disseminate the newest results of research and exchange ideas and concepts the Commission aims to have more meetings in the future. We want to build up active core group ( as large as possible) of corresponding members of the Paleopedology Commission.
2. Inter-Congress meetings.
Two business meetings were held between the 1995 and 1999 INQUA Congresses:
July 1998, the IV International Symposium and Field Workshop on Paleopedology, Lanzhou, China, attended by 48; see Newsletter 15, 1998.
The oral presentations were divided into five sessions on (a) polygenetic concepts of surface (relict) paleosols, (b) recognition, classification and modelling of soils with relict properties, (c) implications of paleosol features for agriculture, forestry and the environment, (d) buried paleosols as a tool for reconstructing and modelling past environmental change, and (e) archeology and dating of paleosols. Refereed papers will be published in a special issue of Catena.
The main conclusions arising from the Working Meeting were that (a) paleopedology can account for many of the features influencing the behaviour of surface soils, which are not explained by the current soil environment, and (b) better studies of current pedogenesis are needed to interpret past climatic change from the long sequences of buried soils preserved in Quaternary loess and other deposits.
The IV International Symposium and Field Workshop on Paleopedology, July 27-30, 1998, Lanzhou, China was sponsored and supported by INQUA, National Natural Science Foundation of China, National Education Commission of China, China Quaternary Commission, China Soil Science Society, Government of Gansu Province and Lanzhou University.
The oral presentations were divided into six sessions on:
(a) Genesis of Late Pleistocene and Holocene Soils in relation to environmental change.
(b) Pedological signals of millennial climatic fluctuations.
(d) Quantification of biotic and abiotic soil / paleosol properties used as indicators of paleoclimate and geomorphological evolution.
(f) Cenozoic magneto-, bio- and pedostratigraphy and long - term climatic change.
About 30 participants from China and about 35 participants from 11 foreign countries discussed the oral and poster presentations summarized in a book of abstracts. From a paleopedologic point of view the papers dealing with magnetic properties of loess - paleosol sequences in different parts of the world and presented in session C were of special importance. The question whether special kinds of magnetic susceptibility (MS) can be regarded as a climatic proxy, highlighting the problem of lithogenic versus pedogenic MS, created a fruitful discussion. The meeting was accompanied by an extensive field program: a pre-Conference tour (July 17 -26,1998) from Kashgar to Urumqi, Xinjiang; a one day mid-Conference excursion in the vicinity of Lanzhou; and a eight-day post-Conference tour from Lanzhou via the western loess hill country, the north-eastern Tibetan Plateau and the West Quinling Mountains to Lanzhou. Cliff Ollier and E. Bibus in NL-15 gave reports of this meeting.
A Paleopedology Symposium entitled Records in Soils of Environmental
and Anthropogenic Changes was held at the 16th International Soil Science
Congress, July, Montpellier, France, and was organized by John Catt and
Nicholas Fedoroff on behalf of IUSS Commission V (Soil Genesis, Classification
and Cartography) and Working Group PP (Paleopedology). The symposium was
concerned with the effects of environmental factors on soil properties
and with reconstructing past environments from soil properties. These are
subjects of increasing importance, the first because of the concern that
man increasing influence on global environments is seriously limiting
the capacity of soils to produce food for a rapidly expanding world population,
and the second because knowledge of how environmental changes occurred
in the past is important for predicting future global environmental change.
Oral contributions were complemented by poster session (see report in NL-15),
and both will be published in special issues of Catena and Quaternary
Contributions of Commission meetings have been published in three volumes:
1.Reviewed manuscripts of the II International Symposium and Field workshop (Champaign-Urbana, USA, 1993) came out in Quaternary International, Vol. 51/52 at the end of 1998. Besides 13 full papers (pp. 87 -221) this contains numerous short papers including propositions (position statements etc.), essays (free style discussion of a subject deemed important) and abstracts.
2. Twelve reviewed papers originally presented at a symposium of the XIV INQUA Congress 1995 in Berlin entitled Reconstruction and Climatic Implications of Quaternary Paleosol Sequences organized by the PP-Commission came out in a special issue of Catena in 1998 (vol.34, pp. 1-207).
3. Due to considerable effort of Prof. X-M Fang, thirty-eight
reviewed papers, mainly presented at the IV ISFWP (Lanzhou, China, 1998)
were published in Chinese Science Bulletin in July 1999 (vol.44,
Supplement 1, pp. 1-263). Copies were distributed among participants of
INQUA Congress in Durban.