soils in archaeological research aug 2004

Soils in Archaeological
Research

Vance T. Holliday

OXFORD UNIVERSITY PRESS


SOILS IN ARCHAEOLOGICAL RESEARCH


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SOILS IN ARCHAEOLOGICAL RESEARCH

Vance T. Holliday

1
2004


3

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Library of Congress Cataloging-in-Publication Data
Holliday, Vance T.
Soils in archaeological research / by Vance T. Holliday.
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Includes bibliographical references and index.
ISBN 0-19-514965-3
1. Soil science in archaeology. I. Title.
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To my pedologic mentors: B. L. Allen and Peter W. Birkeland

(Left) B. L. Allen in the field on the High Plains, 2002. (Right) Pete Birkeland at the Geological Society of America Penrose Conference on Paleosols, Oregon, 1987.


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Preface

This book is a discussion of the study of soils as a component of earth science
applications in archaeology, a subdiscipline otherwise known as geoarchaeology.
The volume focuses on how the study of soils can be integrated with other aspects
of archaeological and geoscientific research to answer questions regarding the
past. To a significant degree, the book approaches soils as a function of and as
clues to the factors of soil formation; that is, the external or environmental factors
of climate, organisms, relief, parent material, and time (making up the well-known
CLORPT formula of Jenny, 1941; discussed in chapter 3) that drive the processes
of soil formation. Reconstructing the factors is important in reconstructing the
human past. The book outlines the many potential and realized applications of
soil science, especially pedology and soil geomorphology, in archaeology. This
approach contrasts with earlier systematic, single-author volumes on the topic
(Cornwall, 1958; Limbrey, 1975). The older works tend to emphasize human
impacts on soils, particularly from an agricultural perspective, which is not surprising given their focus on northwest Europe. Moreover, soil geomorphology
was essentially unrecognized when Cornwall’s classic study was published and
was just beginning to come into its own as a subdiscipline when Limbrey’s book
appeared.
The volume is designed for use by students and professionals with backgrounds in both archaeology and earth science, particularly pedology, geomorphology, and Quaternary stratigraphy. The target audience is the archaeologists
and geoarchaeologists who want to know how soils can be used to aid in answering archaeological questions. In addition, I hope this book will help pedologists
and soil geomorphologists understand more about investigating the human past.


viii

PREFACE

A few basic concepts and principles in pedology are presented as necessary. More

attention is devoted to theoretical, conceptual, and especially practical issues in
soil geomorphology because few students or professionals in archaeology and in
the geosciences have access to training in soil geomorphology and because a
variety of issues in soil geomorphology are of direct relevance to geoarchaeology. However, this book is not an introductory text to pedology or soil geomorphology. Some of the world’s leading investigators in these disciplines have
already prepared good introductions, including Buol et al. (1997) and Fanning
and Fanning (1989; for U.S. views of pedology); Birkeland (1999) and Daniels
and Hammer (1992; for North American approaches to soil geomorphology);
Fitzpatrick (1971), Duchaufour (1982), Gerrard (2000), and Van Breemen and
Buurman (2002; for British/European perspectives on pedology); and Gerrard
(1992; for a British/European view of soil geomorphology). These summaries, and
for that matter this volume, are no substitute for formal instruction and practical field experience, however. Pedology, soil geomorphology, and geoarchaeology
are all “hands-on” field disciplines.
Field experience and instruction applies to geoscientists interested in archaeology as well as to archaeologists who want to use soils in their research, a point
raised in one of the earliest papers on soils in archaeology (Cornwall, 1960, p.
266). Such training is an essential key to mutual understanding. Lack of communication or, more typically and specifically, the inability to communicate
between archaeologists and geoscientists (or any other scientists outside of mainstream archaeology), despite the best of intentions, is a frequent source of frustration and tension on interdisciplinary archaeological projects. A personal
experience illustrates the point. I was briefly involved in an archaeological survey
that included a well-respected soil scientist who had just retired from the Soil
Conservation Service (now the National Resource Conservation Service). The
archaeologist in charge was quite excited at the prospect of having this veteran
pedologist on the team, though was vague when I asked what results were
expected of the pedologist. The pedologist was, in private conversations with me,
equally bewildered in regard to his duties and the larger archaeological efforts,
but decided he would just do what he knew best. The end result was a frustrated
archaeologist with an excellent soil map of the project area, but a map containing little information of archaeological or geomorphological significance. I hope
this volume serves to facilitate communication between archaeologists and soil
scientists or other geoscientists and will help investigators minimize or avoid
similarly frustrating situations.
Geoarchaeologists must understand the questions asked in archaeology and
must also understand that, unfortunately, geoscience training is not a common

component of most archaeology degree programs. Archaeologists, in turn, must
understand that the utility of soils in archaeology goes beyond knowing how to
describe or classify them and goes beyond knowing some laboratory techniques.
I have worked with archaeologists—good ones—who could identify an A or Bt
horizon in the field and who could tell me that their site area was mapped as a
Haplustalf, but who were otherwise clueless as to the stratigraphic, chronologic,
or geomorphic implications of these soil characteristics. Field description and
classification are simply means to an end.


PREFACE

ix

In an attempt to resolve some of these problems, I have written a book that
pulls together my own ideas and those of many others regarding the role that
soil science and particularly pedology can play in archaeological research. This
approach is based on my own training and experience as well as that of colleagues
in soil geomorphology, geoarchaeology, and archaeology. Some of the examples
are not related to archaeological research because so little of this type of soils
work has been done in archaeological contexts, but these examples illustrate the
principles and the potentials for archaeology.
The first three chapters of the volume present introductory discussions of soils
in geoarchaeology and basic concepts (chapter 1), basic terminology and methods
of studying soils (chapter 2), and theoretical or conceptual aspects of soil genesis,
including further discussion of the CLORPT approach to soil geomorphology
(chapter 3). The next three chapters deal with two fundamental applications of
soils in geoarchaeological research: soil surveys (chapter 4) and soil stratigraphy
(chapters 5 and 6). In a sense, soil survey involves the landscape or relief factor
and soil stratigraphy the parent material factor, though both components of soil

investigation involve aspects of the other factors. Chapters 7 through 9 are more
explicitly organized around the soil-forming factors: the concept of time in pedogenesis and soils as age indicators (chapter 7); soils as indicators of past climate
and vegetation (chapter 8); and soils as related to and indicators of relief and
landscape evolution (chapter 9). The final two chapters discuss soils in the context
of investigations that have been more commonly an explicit component of
archaeological research: site-formation processes (chapter 10) and land use and
human impacts on the landscape (chapter 11). Three appendixes are also provided: 1, on variations to the standard U.S. Department of Agriculture soilhorizon nomenclature useful in soil geomorphic and geoarchaeological research;
2, on comparisons of some common laboratory methods for analysis of soils in
archaeological contexts; and 3 (with coauthors Julie Stein and Bill Gartner), on
comparisons of some common laboratory methods for analysis of soils in archaeological contexts.
This book is written from a geoscience perspective. Conventions regarding age
estimates and chronostratigraphy, therefore, follow geologic standards. Ages of
less than 100,000 yr are expressed in “yr B.P.” as are uncalibrated radiocarbon
ages unless otherwise noted. Ages of 100,000 yr or older are expressed as “ka”
(thousands of years) or “Ma” (millions of years). The age of the Plio-Pleistocene
boundary is placed at 1.8 Ma (Harland et al., 1990; Pasini and Colalongo, 1997)
and the age of the Pleistocene-Holocene boundary is 10,000 yr B.P. (after
Hageman, 1972). The early-middle Pleistocene boundary (equivalent to the
early-middle Quaternary boundary) is placed at the Brunhes-Matuyama polarity reversal, 788 ka (after Harland et al., 1990, p. 68, sec. 3.21.2). The middle-late
Pleistocene boundary (equivalent to the middle-late Quaternary boundary) is
placed at the beginning of marine oxygen isotope stage 5e (after Harland
et al., 1990, pp. 68–69, sec. 3.21.2), which represents the beginning of the last interglacial period before the Holocene, dated to ca. 125 ka (following Winograd
et al., 1997).
This book began to take shape when I was a Visiting Professor at the Alaska
Quaternary Center at the University of Alaska–Fairbanks (spring 1994). Jim


x

PREFACE

Dixon and Mary Edwards helped significantly in arranging my stay in Fairbanks.
The next phase of writing began during a sabbatical leave granted by the College
of Letters and Sciences of the University of Wisconsin–Madison (fall 2000).
I appreciate the help of many individuals who supplied line drawings and photographs that appear in this book and who allowed the photographs to be reproduced: Art Bettis, John and Bryony Coles, Jonathan Damp, Rick Davis, Ed Hajic,
John Jacob, Jim Knox, Rolfe Mandel, Charlie Schweger, Marc Stevenson, Mike
Wiant, and Don Wyckoff.
The line drawings and most of the photographs were prepared with support
from the Cartography Laboratory of the Department of Geography at the University of Wisconsin–Madison. My gratitude to Onno Brouwer, director of the
Cartography Laboratory, for his generous support. This chore was patiently and
expertly carried out by Rich Worthington and Erik Rundell. Laura Pitt (University of Wisconsin) prepared many of the tables. Dirk Harris (University of
Arizona) helped prepare some of the photo scans. Additional support for
preparation of the artwork was provided by the Office of the Provost of the
University of Arizona.
This book has its roots in my initial experience with and thoughts about soils
in archaeological contexts in the 1970s and in a few subsequent attempts to organize my thinking on the subject (Holliday, 1989a, 1990a). Many people, some who
became good friends and close colleagues, have directly or indirectly influenced
my experiences and ideas regarding soils in archaeology, and I take great pleasure in acknowledging them here. My initial exposure to soils came when I
started working on the Lubbock Lake Project (run under the auspices of the
Museum of Texas Tech University) as a research assistant (1974–1978) in the
Museum Science graduate program. As I became familiar with the remarkable
soils record at Lubbock Lake and took my first soils courses, my budding interests were encouraged by Chuck Johnson and especially by Eileen Johnson, who
were codirecting the project. However, the person key to pushing me in the direction I took was B. L. Allen, Professor (now Emeritus) of Soil Science at Texas
Tech: one of this country’s great pedologists, an outstanding teacher and mentor
and one of Texas’s fine, decent gentlemen. I took all of my basic soils training
from B. L., but more than that, he shared an interest in archaeology and in the
record of the past that soils contain. We began work together on the soils at
Lubbock Lake, and he enthusiastically encouraged me to pursue these investigations for a Ph.D. As a result, I entered the graduate program in Geological
Sciences at the University of Colorado (1978) to work on a doctoral dissertation
under Peter W. Birkeland (now Professor Emeritus).

My four and half years at the University of Colorado were one of the great
experiences in my professional career. The faculty and students in the department, and Pete Birkeland in particular, instilled and inspired my approach to soil
geomorphology, Quaternary geology, and the academic life. Pete is an amazing
individual, both as a scientist and a friend, with his laid-back style, deep concern
for students and teaching, and substantial research productivity. Studying with
him is one of my proudest accomplishments.
After graduate school I spent two years at Texas A&M University in the
departments of Geography and Anthropology. There I had the opportunity to


PREFACE

xi

get to know two other great pedologists: Larry Wilding and Tom Hallmark.
Discussions with both of these men, and some enjoyable fieldwork with Tom,
provided valuable insights into soil-forming processes and how they might be
important in archaeological research.
Most of my postgraduate career until 2002 was in the Department of Geography at the University of Wisconsin–Madison. My approach to soil stratigraphy,
soil geomorphology, and soil investigations in archaeological research gelled
during my 16 years at the UW. I benefited greatly from many discussions with
my colleagues there: Jim Knox, Tom Vale, Karl Zimmerer, and the late Francis
Hole (all in Geography), and Kevin McSweeney and Jim Bockheim (both in Soil
Science). The real learning came in teaching classes and seminars and working
in the field with graduate students. Those particularly interested in soils and
geoarchaeology and who expanded my pedoarchaeological horizons include
John Anderton, Mike Daniels, Bill Gartner, Peter Jacobs, Jim Jordan, Samantha
Kaplan, David Leigh, Joe Mason, James Mayer, Jemuel Ripley, Garry Running,
Ty Sabin, and Catherine Yansa (in Geography); Danny Douglas, Jeff Monroe,
and Jesse Rawling (in Geology); Steve Cassells, Pat Lubinski, Bill Middleton,

Megan Partlow, Jeff Shockler, and Tina Thurston (in Anthropology); and David
Brown (in Soil Science).
Over the years I’ve met many other colleagues who share my interests in using
soils to unravel the human past. We’ve talked and corresponded, coauthored
papers, coedited books, worked in the field, and in some fortunate situations
become friends. All have influenced my thinking about this topic, and with great
pleasure I acknowledge and thank them: Art Bettis, Andrei Dodonov, Bill
Farrand, Paul Goldberg, Ed Hajic, Rich Macphail, Les McFadden, Rolfe Mandel,
Dave Meltzer, Dan Muhs, Lee Nordt, Julie Stein, and Dan Yaalon. A number of
colleagues very kindly and very helpfully reviewed chapters: Art Bettis (chapters
1 through 6), Paul Goldberg (chapters 1 and 11), Jeff Homburg (chapter 11), Rich
Macphail (chapter 11), Rolfe Mandel (chapters 1, 2, 5, and 6), Lee Nordt (chapters 1, 7, 8, 9, and 10), Mike Schiffer (chapter 10), and Bill Woods (chapters 1 and
10). James Mayer helped with statistical analyses of the radiocarbon ages
(chapter 7). Thanks also to Julie Stein and Bill Gartner for collaborating on
appendix 3. Additional information, commentaries, or data were provided by
Jesse Ballenger, Pete Birkeland, Glen Doran, Charles Frederick, Bill Johnson,
Don Johnson, Rob Kemp, Mike Kolb, Mary Kraus, Johan Linderholm, Randy
Schaetzl, Russell Stafford, Julie Stein, Gregory Vogel, and Don Wyckoff. Jim
Burton, Phil Helmke, Tina Thurston, and Bill Woods also helped me out on the
ticklish topic of soil phosphorus.
Finally, my deep gratitude to two lovely ladies—my wife Diane and my daughter Cora—for their patience during this long writing process.


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Contents

1 Introduction

1

2 Terminology and Methodology

13

3 Conceptual Approaches to Pedogenesis
4 Soil Surveys and Archaeology
5 Soil Stratigraphy

41

53

72

6 Soil Stratigraphy in Geoarchaeological Contexts
7 Soils and Time

97

139

8 Soils and Paleoenvironmental Reconstructions
9 Soils and Landscape Evolution

232

10 Soil Genesis and Site-Formation Processes
11 Human Impacts on Soils

290
xiii

261

188


xiv

CONTENTS

Appendix 1: Variations on U.S. Department of Agriculture Field
Nomenclature 338
Appendix 2: Soil Phosphorus: Chemistry, Analytical Methods, and
Chronosequences 343
Appendix 3: Variability of Soil Laboratory Procedures and Results
with Julie K. Stein and William G. Gartner

References
Index

435

375

363

SOILS IN ARCHAEOLOGICAL RESEARCH


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1

Introduction

Soils are a potential source of much information in archaeological studies on siteand feature-specific scales as well as on a regional scale. Soils are a part of the
stage on which humans have evolved. As an integral component of most natural
landscapes, soils also are an integral component of cultural landscapes. “Soils are
active components of functioning ecosystems that reflect the spatial variability
of ecological processes and at the same time have varying degrees of suitability
for different kinds of human behavior” (Warren, 1982b, p. 47). Beyond physically
supporting humans and their endeavors, however, soils are indicators of the
nature and history of the physical and human landscape; they record the impact
of human activity, they are a source of food and fuel, and they reflect the environment and record the passage of time. Soils also affect the nature of the cultural record left to archaeologists. They are a reservoir for artifacts and other
traces of human activity, encasing archaeological materials and archaeological
sites. Soil-forming processes also are an important component of site formation
processes. Pedogenesis influences which artifacts, features, and environmental
indicators (floral, faunal, and geological) are destroyed, which are preserved, and
the degree of preservation.
Those involved in field archaeology (as archaeologists, geoscientists, or bioscientists) routinely deal with soils—probably more so than most soil scientists
or geologists (Birkeland, 1994, p. 143). However, what the soils or a soil scientist
can tell archaeologists about the site and about the archaeological record is not
always clear. In part, the integration of soil science in archaeology has been hampered by ambiguities in use of the term “soil” and confusion over what a soil is
or is not. The bigger issue is that pedological research, particularly in the United
1

2

SOILS IN ARCHAEOLOGICAL RESEARCH

States, has not traditionally been a component of geoarchaeology (the application of the earth science in archaeology) until recent years, in comparison with
applications of other aspects of geoscience such as stratigraphy, sedimentology,
or geomorphology. This situation evolved in large part because the academic
study of soils typically is located in the agricultural sciences rather than the earth
sciences. Students of archaeology and the geosciences, therefore, often have no
access to courses in soil science because agriculture programs are considerably
less common than schools of arts and sciences. As Tamplin (1969, p. 153) noted,
most archaeologists are well trained in the principles of stratigraphy and the
“Law of Superposition” long before they learn about soils and soil formation.
Further compounding the problem is the focus of most soil science training and
research, which is on mapping, contemporary land use, soil quality, and plant productivity and not on reconstructing the past (Tandarich and Sprecher, 1994;
Bronger and Catt, 1998a; McFadden and McDonald, 1998; Holliday et al., 2002).
Soil scientists are often unfamiliar with questions of concern to archaeologists,
geologists, and geographers—questions of stratigraphy, landscape evolution, and
paleoenvironments. In addition, U.S. pedologists seldom gain experience in
dealing with extensively altered soils such as middens and plaggens because they
are rare or of limited extent in North America and are therefore of limited interest in terms of mapping and land use.

Soil Science, Soils, and Soil Horizons
Before continuing into the substance of this chapter, some fundamental disciplinary and conceptual issues must be reviewed. This book is an application of subfields of soil science in archaeology and geoarchaeology. Soil science is the study
of soils as a natural resource on the Earth’s surface and includes the study of soil
formation, classification and mapping, soil chemistry, soil physics, soil biology, and
soil fertility (Soil Science Society of America, 1987, p. 24). The principal subfields
of soil science that are the focus of this book are pedology and soil geomorphology, both of which overlap with the disciplines of geology and physical geography. Pedology is the study of soils as three-dimensional bodies intimately

related to the landscape, focusing on their morphology, genesis, and classification.
Soil geomorphology is the study of relationships between soils and landscapes
(e.g., Ruhe, 1956, 1965; Daniels and Hammer, 1992; Gerrard, 1992; Birkeland,
1999). In its broadest sense, soil geomorphology is the investigation of soils as
they were influenced by climate, flora, fauna, topography, and geologic substrate
operating over time (e.g., Birkeland, 1999).
What Is a Soil?
The word “soil” is used by different individuals in different ways. To the farmer,
the agricultural scientist, and some soil scientists, it is simply the medium for plant
growth. To the engineer, some geologists, and probably many archaeologists, it is
unconsolidated sediment including loose or weathered rock or regolith. To the
pedologist and soil geomorphologist, however, soil has a very specific definition


INTRODUCTION

3

that is not always properly understood or appreciated. Using this definition, a
soil is a natural three-dimensional entity that is a type of weathering phenomena
occurring at the immediate surface of the earth in sediment and rock, acting as
a medium for plant growth, and the result of the interaction of the climate, flora,
fauna, and landscape position, all acting on sediment or rock through time (modified from Soil Science Society of America, 1987). The medium for soil development (i.e., the rock or sediment in which the soil forms) is referred to as “parent
material.”
Key concepts in the pedologic and soil geomorphic view of soils are that, first,
soils form in or represent an alteration by physical, chemical, and biomechanical
weathering of sediments and rocks over time (i.e., soils are a type of surface
weathering phenomena); second, pedogenesis includes interaction with flora and
fauna and accumulation of organic matter; third, there is some movement or
redistribution (typically downward, but also upward) of clastic, biochemical, and

ionic soil constituents (e.g., clay, organic carbon, iron, aluminum, and manganese
compounds, and calcium carbonate in ionic solution); fourth, soils are an intimate
component of the landscape, form on relatively stable land surfaces, and are
approximately parallel to the land surface; fifth, soils are dynamic and are components of the ecosystem representing the interface of the atmosphere, the biosphere, and the geosphere; and sixth, soils are extremely complex systems.
Soils are laterally extensive across the landscape. They form across various
landforms and in a variety of parent materials and vary in a predictable manner
because of changes in erosion, deposition, drainage, vegetation, fauna, and age of
the landscape. Soils also vary as the microclimate and macroclimate varies. This
predictable variability is referred to as the “constancy of relationships” (Brewer,
1972, p. 333) and is unique to soils among geomorphic phenomena. This characteristic of soils in buried contexts allows them to be traced in three dimensions
over varying paleotopography. Individual layers of sediment, in contrast, will be
confined to particular depositional environments and will thin to nothing away
from that environment (Mandel and Bettis, 2001b, p. 180).
Soil Horizons
“Soil horizons” are zones within the soil (i.e., subdivisions of the soil) that parallel the land surface and have distinctive physical, chemical, and biological properties (table 1.1; fig. 1.1). Soil horizons result from mineral alteration, biogenic
activity, additions of organic matter, leaching of soluble materials, and translocation of fine particles, humus, and chemical compounds (table 3.1; fig. 3.1).
Together, a set of genetically related horizons produce a “soil profile.” A
soil profile is the vertical arrangement of soil horizons, typically seen in a twodimensional exposure down to and including the parent material (fig. 1.1), similar
to a standard archaeological profile—which may exhibit a soil profile. Soil profiles vary because of the complex interaction of climate, the biota living on and
in the soil, the nature of the soil parent material, the landscape position, and the
age and evolution of the landscape (i.e., the soil-forming factors, discussed in
chapter 3). The “solum” is the upper and most weathered part of the soil profile,
the A, E, and B horizons. A “sequum” is an eluvial horizon (e.g., E) and an


Table 1.1. General definitions of soil horizons used in the United States
Soil Master Horizons
O horizon or layer: Horizons or layers dominated by organic material. Some are saturated with
water for long periods or were once saturated but are now artificially drained; others were
never saturated. Some O horizons consist of undecomposed or partially decomposed litter,

such as leaves, needles, twigs, moss, and lichens, that were deposited on the surface; they may
be on top of either mineral or organic soils. Other O layers are organic materials that were
deposited under saturated conditions and have decomposed to varying stages.
A horizon: Mineral horizon that formed at the surface or below an O horizon and that exhibits
1) obliteration of all or much of the original rock structure and 2) an accumulation of
humified organic matter intimately mixed with the mineral fraction.
E horizon: Mineral horizon in which the main characteristic is loss of silicate clay, iron,
aluminum, or some combination of these, leaving a concentration of sand and silt particles.
This horizon exhibits obliteration of all or much of the original rock structure. An E horizon is
usually lighter in color than an overlying A horizon and an underlying B horizon. In some
soils the color is that of the sand and silt particles, but in many soils coatings of iron oxides or
other compounds mask the color of the primary particles.
B horizon: Horizon that forms below an A, E, or O horizon and is dominated by obliteration of
all or much of the original rock structure and shows one or more of the following: 1) illuvial
concentration of silicate clay, iron, aluminum, humus, carbonates, gypsum, or silica, alone or in
combination; 2) evidence of removal of carbonates; 3) coatings of sesquioxides that make the
horizon conspicuously lower in value, higher in chroma, or redder in hue than overlying and
underlying horizons without apparent illuviation of iron; 4) alteration that forms silicate clay
or liberates oxides or both and that forms granular, blocky, or prismatic structure; or 5)
brittleness.
C horizon or layer: Horizon or layer, excluding hard bedrock, that is little affected by pedogenic
processes and lack properties of O, A, E, or B horizons. The material of C layers may be
either like or unlike that from which the solum formed. The C horizon may have been
modified even if there is no evidence of pedogenesis. Included as C layers are sediment,
saprolite, unconsolidated bedrock, and other geologic materials that commonly are
uncemented.
R layers: Hard (minimally weathered) bedrock.
Horizons dominated by properties of one master horizon but having subordinate properties of
another: Two capital letter symbols are used: AB, EB, BE, or BC. The master horizon symbol
given first designates horizon whose properties dominate the transitional horizon (e.g., an AB

horizon has characteristics of both an overlying A horizon and an underlying B horizon, but it
is more like the A than like the B).
Horizons in which distinct parts have recognizable properties of the two kinds of master horizons
indicated by the capital letters: The two capital letter are separated by a virgule(/): E/B, B/E, or
B/C. Most of the individual parts of one of the components are surrounded by the other.
Subhorizons or Subordinate Horizons of Master Horizons
a

b

c

Highly Decomposed Organic Material: Used with “O” to indicate the most highly
decomposed of the organic materials. The rubbed fiber content is less than about 17 percent
of the volume.
Buried Soil or Horizon: Used in mineral soils to indicate identifiable buried horizons with
major genetic features that were formed before burial. Genetic horizons may or may not
have formed in the overlying material, which may be either like or unlike the assumed
parent material of the buried soil.
Concretions or Nodules: Indicate a significant accumulation of cemented concretions or
nodules. The cementing agent is not specified except it cannot be silica. This symbol is not
used if concretions or nodules are dolomite or calcite or more soluble salts, but it is used if

4


Table 1.1. (cont.)

d

e

f

g

h

i
k
m

n
o
p

q
r

s

ss
t

the nodules or concretions are enriched in minerals that contain iron, aluminum, manganese,
or titanium.
Physical Root Restriction: Indicates root-restricting layers in naturally occurring or
manmade unconsolidated sediments or materials such as dense basal till, plow pans, or other
mechanically compacted zones.
Organic Material of Intermediate Decomposition: Used with “O” to indicate organic

materials of intermediate decomposition. Rubbed fiber content is 17 to 40 percent of the
volume.
Frozen Soil: Indicates that the horizon or layer contains permanent ice. Symbol is not used
for seasonally frozen layers or for “dry permafrost” (material that is colder than 0°C but
does not contain ice).
Strong Gleying: Indicates either that iron has been reduced and removed during soil
formation or that saturation with stagnant water has preserved a reduced state. Most of the
affected layers have chroma of 2 or less and many have redox concentrations. The low
chroma can be the color of reduced iron or the color of uncoated sand and silt particles
from which iron has been removed. Symbol “g” is not used for soil materials of low chroma,
such as some shales or E horizons, unless they have a history of wetness. If “g” is used with
“B,” pedogenic change in addition to gleying is implied. If no other pedogenic change in
addition to gleying has taken place, the horizon is designated Cg.
Illuvial Organic Matter: Used with “B” to indicate the accumulation of illuvial, amorphous,
dispersible organic matter-sesquioxide complexes. The sesquioxide component coats sand
and silt particles. In some horizons, coatings have coalesced, filled pores, and cemented the
horizon. The symbol “h” is also used in combination with “s” as “Bhs” if the amount of
sesquioxide component is significant but the value and chroma of the horizon are 3 or less.
This horizon is not to be confused with the “Ah” used to designate human impacts
(appendix 1).
Slightly Decomposed Organic Material: Used with “O” to indicate the least decomposed of
the organic materials. Rubbed fiber content is more than about 40 percent of the volume.
Carbonates: Accumulation of calcium carbonate.
Cementation or Induration: Continuous or nearly continuous cementation. The symbol is
used only for horizons that are more than 90 percent cemented, although they may be
fractured. The layer is physically root restrictive. If the horizon is cemented by carbonates,
“km” is used; by silica, “qm”; by iron, “sm”; by gypsum, “ym”; by both lime and silica,
“kqm”; by salts more soluble than gypsum, “zm.”
Sodium: Accumulation of exchangeable sodium.
Residual Sesquioxides: Residual accumulation of sesquioxides.

Plowing or Other Disturbance: Disturbance of the surface layer by mechanical means,
pasturing, or similar uses. A disturbed organic horizon is designated Op. A disturbed mineral
horizon is designated Ap even though it was clearly once an E, B, or C horizon.
Silica: Accumulation of secondary silica.
Weathered or Soft Bedrock: Used with “C” to indicate root restrictive layers of soft bedrock
or saprolite, such as weathered igneous rock; partly consolidated soft sandstone; siltstone;
and shale. Excavation difficulty is low or moderate.
Illuvial Accumulation of Sesquioxides and Organic Matter: Used with “B” to indicate the
accumulation of illuvial, amorphous, dispersible organic matter-sesquioxide complexes if
both the organic matter and sesquioxide components are significant and the value and
chroma of the horizon is more than 3. The symbol is also used in combination with “h”
(“Bhs”) if both the organic matter and sesquioxide components are significant and the value
and chroma are 3 or less.
Slickensides: Presence of slickensides, which result directly from the swelling of clay minerals
and shear failure, commonly at angles of 20 to 60 degrees above horizontal.
Silicate Clay: Accumulation of silicate clay translocated within the horizon or moved into
the horizon by illuviation, or both. At least some part should show evidence of clay
accumulation in the form of coatings on surfaces of peds or in pores, or as lamellae (“clay
bands”), or bridges between mineral grains.

5


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SOILS IN ARCHAEOLOGICAL RESEARCH

Table 1.1. (cont.)
v

w

x

y
z

Plinthite: Presence of iron-rich, humus-poor, reddish material that is firm or very firm when
moist and that hardens irreversibly when exposed to the atmosphere and to repeated
wetting and drying. This horizon is not to be confused with the “Av” used to designate a
vesicular horizon in arid environments (appendix 1).
Development of Color or Structure: Used with “B” to indicate the development of color or
structure or both, with little or no apparent illuvial accumulation of material (see appendix
1 for additional usages).
Fragipan: Genetically developed layers that have a combination of firmness, brittleness, very
coarse prisms with few to many bleached vertical faces, and commonly higher bulk density
than adjacent layers.
Gypsum: Accumulation of gypsum.
Salts More Soluble than Gypsum: Accumulation of salts more soluble than gypsum.

Combinations of Symbols: A B horizon that is gleyed or that has accumulations of carbonates,
sodium, silica, gypsum, salts more soluble than gypsum, or residual accumulation or
sesquioxides carries the appropriate symbol—g, k, n, q, y, z, or o. If illuvial clay is also present,
“t” precedes the other symbol: Btg.
Modified from Soil Survey Division Staff (1993, pp. 118–126). These symbols are used for describing soils in the
field. For more complete definitions see Buol et al. (1997), Birkeland (1999), Schoeneberger et al. (1998), or Soil
Survey Division Staff (1993). Some alternative horizon designations, including those developed outside of the
United States, are presented in appendix 1.

underlying B horizon. Two sequums in a vertical sequence are a “bisequum”

(common in some podzolizing environments; discussed below).
Soil horizons are the most obvious features of soils in the field because of their
unique physical, biological, and chemical characteristics such as structure and
color (fig. 1.1). Moreover, the development of soil horizons is a characteristic of
soils that is unique among geomorphic processes and features. The ability to recognize soil horizons is a key first step in developing the ability to recognize soils.
The visual distinctness of soil horizons and soils is one of the principal reasons
they have long been used as stratigraphic markers. Careful scrutiny and description of soil profiles and horizons (chapter 2) are critical elements of pedology
and require considerable training and practice.
Soil horizon nomenclature includes a few master or major horizons (the wellknown A-B-C sequence), a considerable number of subhorizon symbols that act
as modifiers of the master horizons, and additional descriptive terminology (table
1.1; appendix 1). The soil horizon nomenclature commonly used in the United
States was developed largely by the U.S. Department of Agriculture (USDA)
to meet the requirements of a standardized, nationwide soil survey. This system
is fully explained by the Soil Survey Division Staff (1993; available at
) and Schoeneberger et al. (1998). Excellent summaries are
provided by Buol et al. (1997), Birkeland et al. (1991), and Birkeland (1999).
Vogel (2002) and Reed et al. (2000) have prepared very handy booklets on soil
description for archaeologists. The Soil Science Society of America also has a
very useful glossary of soil science terms ( Canadian terminology is presented by Soil Classification Working Group (1998), and
the Australian nomenclature is described by McDonald et al. (1998). For Europe,


Figure 1.1 Examples of various soil types and profile morphologies from North America. (A) Paleustoll (Flatirons series)
formed in alluvium on an early Pleistocene pediment in the Colorado Piedmont, just east of the Rocky Mountain front.
The soil has a thick, dark, surface horizon high in organic matter (a mollic epipedon), classifying it as a Mollisol. The current
climate is semiarid, with a spring-summer rainy season (ustic moisture regime). The soil has a very well expressed (deep
reddish-brown, thick, clay-rich) argillic (Bt) horizon (with intensely weathered gravel), placing it in the “pale” Great Group.
The scale is in feet. (B) Spodosol from the Upper Peninsula of Michigan, illustrating development of the E and Bhs horizons in sandy, glacial outwash. (C) Alfisol (Hapludalf) from southern Michigan illustrating development of A-E-Bt horizonation typical of postglacial soils in the area developed on loess and till (slide 1–6 from the Marbut Memorial Slide set,
Soil Science Society of America; reproduced with permission of the Soil Science Society of America). Scales are in feet.

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SOILS IN ARCHAEOLOGICAL RESEARCH

Hodgson (1997) presents the standards used in Great Britain (see also Catt,
1990), and Duchaufour (1998, pp. 146–147, 148) and van Breemen and Buurman
(2002, pp. 141, 365–366) summarize the Food and Agriculture Organization
of the United Nations (FAO-UNESCO) system (to be updated and superceded
by the FAO World Reference Base for Soil Resources [FAO-WRB]; see
Duchaufour, 1998, pp. 151–152) employed throughout continental Europe (see
Driessen and Dudal, 1991). All of these sources also provide additional specifics
on the terminology and data necessary to describe soils. Some additional nonstandard (i.e., non-USDA-approved) horizon nomenclature, developed by soil
geomorphologists and Quaternary geologists, or by pedologists in other countries, is also provided in table 1.1 and discussed in appendix 1. The USDA horizon
nomenclature, with modifications described in appendix 1, is used throughout this
volume. Older or foreign nomenclatures used in sources for figures and tables
were converted, unless noted.
To fully understand late-20th-century and contemporary USDA-based pedology, the concept of the “pedon” must be noted. The pedon is the smallest body
of one kind of soil large enough to represent the nature and arrangement of horizons (Soil Survey Division Staff, 1993, p. 18). Essentially, the pedon is the soil
profile in three dimensions; a conceptual unit of soil defined for sampling purposes (see Schelling, 1970, p. 170; Buol et al., 1997, pp. 36, 43–44; Soil Survey Staff,
1999, pp. 10–14). Whereas the pedon is conceptual, the “soil individual” (or
“polypedon”) is a real body of soil on the landscape (essentially, more than one
pedon; Schelling, 1970, pp. 170–171; Buol et al., 1997, pp. 36–37). These terms and
definitions are obscure and somewhat unfathomable, and the concepts have little
relevance to geomorphology or geoarchaeology; they are mentioned because
they are key concepts in USDA soil mapping (chapter 4).
Soil Horizons versus Geologic Layers
Soil horizons are not the same as geologic layers. Soil horizons form in geologic
layers. Learning how to distinguish between soil horizons and unaltered sediments is another important step in learning how to recognize soils (Stein, 1985,
p. 6; Mandel and Bettis, 2001b, p. 175). The use of the term “layer” interchangeably with “horizon” in some literature (including soil science publications) is particularly unfortunate and further confuses the issue of differentiating soils from

sediments (Wilson, 1990, pp. 61–62, 71). Geologic layers follow the Law of Superposition: they are deposited one atop the other, with the bottom layer being the
oldest and the top layer the youngest. Soil horizons are superimposed over, and
thus postdate, the geologic materials in which they form (their parent material),
and in general, horizons develop from the top of their parent materials downward (see chapter 5 and Cremeens and Hart, 1995). The boundaries between soil
horizons, therefore, typically have no relationship to geological layering (discussed further in chapter 5). An individual soil horizon can form through several
depositional layers, and conversely, several horizons can form within a single
deposit.
Distinguishing between horizons and geologic layers sometimes is difficult
(discussed further in chapters 5 and 10), particularly given the heavy emphasis