Guidelines for Analysis and Description of Soil and Regolith Thin Sections

Georges Stoops

• Publisher: ACSESS
• Year: 2021
• ISBN:
  9780891189923
• Edition: 2
• Topic: Tecnologia e ingegneria
• Subtopic: Agronomia

A revised guide to the study and of soil and regolith thin sections

A specialized system of terms and concepts must be used to accurately and effectively distinguish and name the microscopic features of soils and regoliths. With a comprehensive, consistent terminology at their disposal, researchers may compare, store and discuss new data easily and with less risk of error. The second edition of Guidelines for Analysis and Description of Soil and Regolith Thin Sections has been assembled to address this need, offering a practical system of analysis and description to those working with soil and regolith materials.

This essential resource includes:

• An introduction to micromorphology and its practice
• Guidelines for the study of thin sections
• Sections covering the various microscopic features of soils and regoliths
• Illustrative graphics and colour micrographs
• Suggested description schemes and data presentation tips

By providing an economical, navigable system for the study and documentation of soils and regoliths, Guidelines for Analysis and Description of Soil and Regolith Thin Sections, second edition, offers invaluable guidance for soil scientists, geologists, ecologists, archaeologists and all those concerned with micromorphology.

1. Introduction

Precise descriptions of the features seen in soils or regoliths as examined under the microscope require a specific set of concepts and terms because the microscope reveals features that simply cannot be seen with the naked eye. Microscopic features can of course be described using common words, but this would lead to very tedious and lengthy descriptive texts that are time consuming both to write and to read and not always unambiguous. Moreover, it would be difficult to translate such descriptions without losing information or committing errors. By using a comprehensive terminology, descriptions would be not only shorter, but also easier to compare and to store in databases.

Terminology is in the first place a means of communication and, in the second place, a means of education‐ people more easily recognize objects, features, or situations for which they know a name. Features or combinations of features without a name are often not consciously observed! For instance, Inuits have many words for snow, while speakers of English have only one and can barely differentiate between wet and dry snow. Eunologues can distinguish and name many types of wines, based on the variety of grapes, fermentation and storing, whereas people not acquainted with this terminology can merely recognize red, white, and rosé wines.

To put an end to the proliferation of overlapping or contradictory concepts and terms in micromorphological publications, an international working group was created in 1969, under the auspices of the International Society of Soil Sciences, to establish a simple, comprehensive terminology for the description of soil thin sections. The result of this work was published in the Handbook for Soil Thin Section Description by P. Bullock, N. Fedoroff, A. Jongerius, G. Stoops, T. Tursina and U. Babel in 1985 (hereafter referred to as the Handbook). The book was highly appreciated by the micromorphological community, as it helped solve several problems of description inherent to the then existing systems. It became widely used, both for scientific research and as a teaching aid.

Since the early 1990s the Handbook had been out of print, but the original publisher was not interested in the publication of a second edition. Because of the demand for a new edition and to have the opportunity to amend several errors, contradictions and inconsistencies in the original text, I agreed to prepare a new revised text. The Guidelines for Analysis and Description of Soil and Regolith Thin Sections (hereafter referred to as the Guidelines) appeared in 2003. The text of this book was essentially based on the Handbook (Bullock et al., 1985), and on the author's own series of lecture notes and his experience in research and teaching at the International Training Centre for Post‐Graduate Soil Scientists (Ghent University, Belgium) and during several intensive courses on micropedology in Europe and abroad. For some definitions and concepts, different approaches by other soil micromorphologists, which were discussed by Bullock et al. (1985), were not repeated in the Guidelines. Decisions then made, were adopted without arguments or references. In several places, however, definitions and schemes were discussed in more detail, as experience has shown that students are often puzzled why specific decisions were made.

Not all concepts of the Handbook were as user‐friendly as intended by its authors. Especially in those cases where the distinction between features was partly based on common experience of the authors, some concepts were left unclear (Stoops and Tursina, 1992). Stoops (1998) suggested, therefore, the introduction of a key, which would probably not enhance the scientific level of the system much but would surely contribute to the use of unambiguous concepts and to a higher reproducibility of the descriptions, making it easier to store them in a database.

Almost 15 yr after its publication in 2003 the Guidelines was out of print, and a second, updated edition was urgently needed, as the system of concepts and terms became internationally the standard for micromorphological studies. In this second edition some concepts, giving rise to misunderstanding, are clarified and references to literature updated and extended. Almost no new ideas on description or concepts and terms were published in the last two decades. The concepts of the Guidelines were meanwhile also explained in two manuals: Loaiza et al., (2015) and Simões de Castro and Cooper (2019).

In the 1960s and the 1970s, micromorphology was often related to soil classification and/or related genetic studies. Since that time, application has gone beyond the bounds of traditional soil science as other disciplines discovered the utility of micromorphology. Other frequent users of micromorphology include: Quaternary geologists (e.g., Catt, 1989; Kemp, 1999; Cremaschi et al., 2018), sedimentologists (e.g., Zimmerle, 1991; van der Meer and Menzies, 2011; Menzies and van der Meer, 2018), weathering specialists (e.g., Nahon, 1991; Tardy, 1993; Delvigne, 1998), and especially archaeologists (e.g., Courty et al., 1989; Macphail et al., 1990; Davidson et al., 1992; Goldberg and Macphail, 2006; Macphail, 2008, 2014; Nicosia and Stoops, 2017; Goldberg and Aldeias, 2018; Macphail and Goldberg, 2018).

The objective of this book is to provide a system of analysis and description of soil and regolith materials as seen in thin sections. It is not intended as a manual of micropedology; topics such as sampling, thin section preparation, and interpretation of thin sections are therefore not discussed. Also, no attempt has been made to present proposals for higher levels of classification of microfabrics, as no sufficient agreement exists in the international micromorphological community on how to handle this problem.

In the past, many authors mixed the terminologies of Bullock et al. (1985) with those of Brewer (1964a and 1976), Brewer and Pawluk (1975) and others, without realizing the differences (e.g., differences in basic concepts) and especially without being aware of the false interpretations that might result. It is indeed scientifically incorrect to use a mixture of concepts and terms of different systems, which are not compatible. Is there any soil scientist that would accept a classification proposal for a soil profile, expressed in a mixture of U.S. Soil Taxonomy and WRB criteria and terms? Experience has shown that such a mixture of terms is dangerous and often leads to false statements.

To avoid confusion, some micromorphological concepts, definitions, and terms used by other systems are set off in separate explanatory paragraphs “Background”, as complementary information to the reader, but not as a suggestion for its use as part of the proposed terminology. Where appropriate, concepts and terms are compared with those of other authors, without going into detail. The reader is referred to the original papers, or to Stoops and Eswaran (1986) or Jongerius and Rutherford (1979) for additional information. A complete glossary of existing micromorphological terms is beyond the scope of this textbook.

Terminology and/or classification reflect the state of the art in a given field of science and can therefore only be an approximation. The author is aware that this book is only a next approximation to a completer and more rational micropedological terminology.

2. Definitions and Historical Review

2.1 WHAT IS SOIL MICROMORPHOLOGY?

Soil micromorphology is a method of studying undisturbed soil and regolith samples with microscopic and ultramicroscopic techniques to identify their different constituents and to determine their mutual relations, in space and time. Its aim is to search for the processes responsible for the formation or transformation of soil in general, or of specific features, whether natural (e.g., clay skins, nodules) or artificial (e.g., irrigation crusts, plow pans), and their chronology. Consequently it is an important tool for investigations of soil genesis, classification, or management of soils and regoliths. The technique has also proven its usefulness in other domains, especially paleopedology and archeology.

A bibliometric study by Stoops (2014, 2018) shows that from 1950s onwards the number of micromorphological papers published increased, reaching a maximum of almost 700 during the period 1986 to 1990, decreasing slightly from then on. This decrease, explained mainly by the loss of interest in soil genesis and classification topics (due to shortage of funding) and the fact that discussions on new methods and concepts stabilized, was partly compensated by a gradual increase in the fields of paleopedology and archeology (see also Courty et al., 1989; Nicosia and Stoops, 2017; Adderley et al., 2018; Cremaschi et al., 2018; Fedoroff et al., 2018; Macphail and Goldberg, 2018).

Micromorphological investigations are based on the principles of (i) preservatio...