Clay Fabric/Microstructure
Wen-An Chiou
Materials Characterization Center
and
Department of Chemical Engineering and Materials Science
University of California, Irvine
Irvine, CA 92697-2575
USA
Pan-American Advanced Studies Institute on
Transmission Electron Microscopy in Materials Science
July 13, 2006
Table of Contents
• Introduction
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Soil, sediment and clay materials
Definition
Signature of clay fabric
Concepts of clay fabric
Review of previous research
• Methodology of clay fabric research
– Dehydration
– Clay fabric semi-quantification
• Clay fabric case studies
– Deep sea sediments
– In-situ clay fabric
– Clay fabric from different sediments/environments
• Processes and mechanism of clay fabric
• Summary
• Future research
Soil, Sediment, and Clay Materials
• Soil, to engineers, is any unconsolidated materials
composed of discrete solid particles and interstitial gas
and/or liquids (Sowers and Sowers, 1961). More
specifically, soil has been described as a particulate, multiphase system.
– Particulate: system of soil particles (solids).
– Multi-phase: mineral phase (solids) plus fluid phase (air,
gas, and liquid – the pore fluid).
– Pore fluid and its constituents (salts and organic
compounds) will affect the processed of interaction
between the phases – referred as chemical interaction.
• Sediment, to the geologists, is a deposit formed by the
agents of water, wind, or ice and a product of chemical,
biological, and physical weathering of solid material on the
earth’s surface.
• Soil: generally denotes those residual materials the
accumulate during weathering.
• Soil and sediment are often used interchangeably depend
on the context of discussion.
• The most important and active constituents of a soil
(sediment) are the clays (clay minerals).
What is Clays and Clay Minerals
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Clays are:
Size: less than 2 um in general
Chemistry: phyllosicates with different cations
Crystal structure: monoclinic, triclinic
Morphology: various, depend on the species of clay
Common clay minerals: kaolinite, smectite (montmorillonite),
and illite.
• Other clay minerals: Halloysite, chlorite, vermiculite,
attapulgite, sepiorlite, palygorsite, miexed-layer clays, and
allophane.
• Prior to 1923, clays were thought to be amorphous (Hadding,
1923)
• Reference: Clay mineralogy: Grim, 1968
Special Properties of Clays
• Physical Significance of the Atterberg Limits – a very useful
characteristics of assemblages of soil particles, which in turn is
very useful in engineering practice.
• The limits are based on the concept of a fine-grained soil can exist
in any of four various states depending on its water content.
Very small particles – provide very large surface area
Negatively charged surface – provide very active
surface for chemical interaction
(From Bennett and Hulbert, 1986)
What is Clay Fabric/Microstructure
• Fabric: Any material structure consisting of connected parts; a
fabrication or framework.
• Structure: The configuration of elements, parts, or constituents in
such an entity; organization; arrangement.
• Fabric: As used by sedimentary petrologists, refers to “the orientation in
space of the elements of which a sedimentary rock is composed” (Gary
et al., 1972).
• Fabric element: may be a single crystal, a detrital fragment, a fossil or
any component that behaves as a single unit with respect to an applied
force.
• Clay Fabric: the special distribution, orientation, and particle-toparticles relationship of the <4um solid particles (mainly clay minerals)
in the sediment.
• Clay microstructure: the arrangement of atoms in the crystallographic
structure of an individual clay particle.
Diagram of the fundamental particle units called domains that comprise the
“building blocks” of clay fabric in sediments and rocks. (From Bennett et al., 1991)
Signature of Clay Fabric/Microstrucutre
• Microstrucutre preserved in fine-grained sediments and
rocks may be used to identify and recognize specific
sedimentary environments and processes, thus serving as a
distinct imprint or “signatures” of that environment.
• A few important questions:
– What microfabrics produced in various modern
environment?
– What are the actual processes and mechanisms that
determine clay signatures?
– What fabric signatures are found in shales and how may
they used to provide clues to ancient environments?
– Can shale be classified according to fabric types, which,
in turn, may be used to interpret shale properties?
Major processes and mechanisms that determine microfabric
signatures in the macro and micro geological environments
Processes and mechanisms represents a continuum during the developmental history of
clay sediment and shale microstructure (From Bennett et al., 1991)
Importance of Clay Fabric
• In geological science:
– Understanding of geological
environments, economic
geology, environmental
geology, engineering geology
• In civil engineering:
– Understanding the soil
properties, soil behavior,
foundation and slope stability,
geotechnical properties
• In materials science:
– Understanding the material
properties, manufacturing
• In soil sciences:
– soil stability, agriculture,
Background- Historical Review
(Concept of Clay Fabric)
• The physicochemistry of clays is critical in determining the nature
of clay fabric, especially in the early stage of formation.
• Early Concept:
– Perhaps the earliest concepts of clay fabric from engineering and
geological perspectives were presented by Terzaghi (1925).
– Casagrande (1932)
– “Terzaghi-Casagrande honeycomb structure”
• Clay mineral stick to each other at point
of contact, with forces sufficiently strong
to construct a honeycomb structure, which permits large amount
of water to be enclosed in the voids.
Early Concepts of Clay Fabric
• minerals of chemically sensitive clays are Goldschmidt (1926)
and Lambe (1953)
• Flaky arranged in an unstable “cardhouse structure”.
• Lambe (1953), particle orientation in a dispersed system is a
parallel arrangement(oriented fabric), whereas in a flocculated
system, it is random (cardhouse fabric).
Cardhouse, of saltwater
Cardhouse of freshwater
• Mitchell (1956) pointed out important differences between
dispersed and flocculated clays in relation to their geotechnical
properties.
Later Concepts and Observations
• During the last 20-35 years, studies of clay fabric have gained
momentum with the advent of the electron microscopy, and
renewed interest has resulted in numerous investigation of clay
particle arrangement in sediment by direct observation.
• Rosenqvist set the stage for EM studies of clay fabric conducted
in the 1960s.
• Aylmore and Quirk (1960) proposed the term turbostratic
arrangement for a fabric consisting of domains or stacks
• Keller (1964) described a more open structure, which called as
“bookhouse” fabric or book structure.
• Clay fabric from different environments: fresh water, lake,
marine and deep sea sediments.
• Clay fabric of laboratory simulated geotechnical condition.
Van Olphen proposed various
modes of particles association
when clay particles flocculate:
FF, EF, and EE. EE and EF
produce agglomerates (called
“floc”). The FF association is
termed “aggregation”.
Although apparently those
structures proposed by van
Olphens have not been found
for natural sediments. The
modes, however, do afford a
means of reference for the
study of fabric in natural claywater system.
Techniques and Instrumentation for Clay Fabric
Research
Sampling and subsampling
Fixation
Dehydration
Embedding
Microtoming
Electron microscopy observation
Subsampling
Schematic diagram showing the viewing orientation of embedded
specimen. (A) Side or parallel to core axis view. (B) Top or
normal to core axis view. (C) Random view.
Analytical technique and instrumentation for clay fabric
analysis: Dehydration technique
Analytical technique and instrumentation for clay
fabric analysis: Impregnation, sectioning, and TEM
Quantification of Clay Fabric: A Simple Technique
• Orientation Analysis
• Measurement of elongation
direction of grain projections.
• The direction of elongation was
assumed to be that of two
parallel lines with minimum
separation that can be drawn
tangent to the grain projection.
• General view: 2-3 traverse of
200 counts of clay particles at
low magnification
• Confidence: 3-4 traverse of 100
counts on medium or higher
magnification
• Use computer program, pay
attention to the grey level setting
Graphic Computation and Degree of Orientation
• Specific orientation of each particle was assigned to one of
the eighteen 10o intervals between 0 and 180o.
• Rose (polar coordinate) diagrams were used for the
purpose of comparison.
• Degree of orientation: similar to the idea of grain size
analysis
• Graphic computation: to characterizing degree class
orientations by using the formula developed by Folk and
Ward (1957) for computing sorting. “Degree of Orientation”
~”Sort the Particle Orientation”
Clay particle orientation analysis using simple point
count technique
Point counting – the simplest, fastest, and most accurate measurement
Statistical number for calculation
Case Study I – Clay Fabric of Sediments from
Middle America Trench
Purpose: to delineate the interrelationship between
tectonic, sedimentation, and geotechnical
properties is particular important for areas
subjected to the dynamic affects of convergence.
Study Area and Sampling Site
• Sample: DSDP Leg 66, within the Middle America Trench
complex provided an unique opportunity to investigate these
inter-relationship across the trench.
• Geological setting: Site 488, approximately 4 km from the
trench axis at the base of the trench inner slope. Drilling
penetrated 313 m of middle to upper Quaternary clayey silts,
which overlie 115 m of lower to middle Quaternary clayey
silts interbedded with sand.
Geotechnical Property Summary Profiles, Site 488
- No anomalies in geotechnical properties are evident in the upper
200 m, which can be correlated with the thrust fault evident on the
site survey seismic reflection profiles.
- However, it has identified a nearly
horizontal coherent reflection occurring
very near the depth of the geotechnical
properties anomaly at 235m.
Depth
Porosity H2O
Density
Surface
70%
47%
1.53 mg/m3
210 m
49%
27%
1.75
235 m
35%
14.5% 2.05
300 m
45%
33%
1.88
400 m
15%
1.98
- Core obtained through this zone show steeply dipping and truncated
beds as well as inclined fractures, which suggest deformation resulting
from tectonic or mass movement processes.
Clay Fabric Reflects Geotechnical Properties
180 m (above), preferentially oriented
clay fabric consisting of domains of
clay particles. Probably results from
natural consolidation processes due to
increasing overburden pressure.
220 m and 235 m (anomaly zone),
well defined domains which appear
randomly oriented. Clay fabric
appears more disrupted with fewer
well-defined domains and an increase
in electron dense particles.
385 m (below zone of deformation),
well-defined and highly oriented
domains probably indicative of normal
gravitational compaction processes.
Case Study II – In Situ Clay Fabric of Gassy
Submarine Sediment
• Objectives:
• (1) to delineate clay fabric microfeatures in
sediment samples obtained by the use of a
pressure core barrel;
• (2) to reveal clay fabric in the natural marine
sediments;
• (3) to evaluate the difference in clay fabric
between pressure core barrel samples and
conventional core samples, and to enhance the
understanding of the clay fabric of fine-grained
gassy sediments.
Study Area and Sampling Sites – Mississippi Delta
• One of the most thoroughly investigated marine
environments in the world.
• One of the most productive
areas in petroleum exploration.
Technique of Dehydrating Gassy Sediment at In-Situ Pressure
Pressurized core barrel samples were
brought up, and sampling was carried
out in a hyperbaric chamber.
The most critical steps in preparing
samples for EM studies are the
techniques employed in the
dehydration of wet specimens and the
process of embedding a specimen with
an appropriate medium.
Special pressure vessel for replacing
interstitial water with immediate fluid
before critical point drying under
equivalent in situ down hole pressure.
Clay Fabric Analysis
• Method (A) – down-hole pressure
maintained until the sample was
critical point dried
• Clay fabric characterized by
relatively well-oriented clay
particles or domains, with random
structures occurring only locally.
• Domains: FF clay platelets forming
a nearly perfect stack. Domains
appear to vary over a considerable
range of size.
• Large voids: between clay particles
and domains, and could have been
occupied by gases and/or interstitial
water.
• Rose diagram and clay orientation
frequency curve reveal the
statistical calculation of welloriented clay fabric.
• SEM observation
also reveal fairly
well-oriented nature
of clay platelets
although may not
show as distinctly as
those in TEM
micrograph.
• Statistical analysis of
clay orientation is
difficult based on
SEM results.
• Method (B) – Downhole
pressure was released before
complete dehydration of the
sediment.
• Clay fabric appears from
semi-oriented to fairly
nonoriented microfeatures.
Random fabric were
pedominant in most cases.
• Domains: numerous EE
contacts, and the size of
individual domains decreases.
Particles do not appear to be
in contact with other particles,
but seem to be “floating” in
space.
• Rose diagram: random
arrangement.
• Frequency curve: widely
spread orientation spectrum.
• Method (C) Conventional
method, the downhole pressure
was released before any process
of dehydration of the sample.
• Clay fabric: typified by highly
random arrangement of clay
particles or domains.
• Domains: appear to be “floating”
in space.
• Voids: large and appear to be
very well connected showing
“channel-like” feature. A few
large “pocket-like” pore spaces.
• Orientation analysis: showing
highly random clay particle
arrangement.
• SEM show similar clay
microfeatures.
Method (C):
Conventional
method
Clay Fabric and Shear Strength
Vane shear tests were
performed:
– (1) while at downhole
pressure (in a hyperbaric
chamber)
– (2) in the laboratory after
depressurization
(conventional technique).
– Clay sediment with
preferred orientation
displays high shear
strength, while clay
sediment with random
microstructure has lower
shear strength.
Clay Fabric of Eckernford Bay, Baltic Sea
Surface sediments (195 cm) showing microfabric of open pore network
With aggregates of more closely packed particles.
Clay Fabric and Biological Components
Clay Fabric of Eckernford Bay, Baltic Sea, Sampling depth 1 mm,
showing particle agglomerates about a stained microbial cell.
Clay Fabric and Clay Diagenesis
The microfabric of authigenic
mineralization in a red clay of
the Northwest Pacific deep-sea
basin (22.5 m subbottom) as
observed by TEM.
Note the lacy. Fine divided
crystals that form a very porous
network. The mineral “smectite”
appears to have developed by
expansion of the crystal
network pressing larger crystals
radially outward while
reorienting the larger particles
in a direction normal to the
direction of stress.
Clay Fabric and Clay/Mineral Diagenesis
Clay Fabric and Mineral Diagenesis
Formation of Biosediment Aggregates
(From Bennett et al., 1991)
Major Processes and Possible Mechanisms
Physicochemical Processes
(From Bennett et al., 1991)
Major Processes and Possible Mechanisms
Bioorganic Processes
(From Bennett et al., 1991)
Major Processes and Possible Mechanisms
Burial-diagenesis
(From Bennett et al., 1991)
SUMMARY
A number of subjects that related to clay fabric has been presented
and discussed in this presentation:
(1) The introduction of the concept of clay fabric, and the role of
clay fabric in science and engineering.
(2) The brief review of the development of clay fabric research,
and the methods of preparing samples for clay fabric study in a
TEM.
(3) The results of clay fabric study from different examples, and
possible mechanism of the formation of clay fabric.
(4) The demonstration of the importance of clay fabric in the
different fields of science/engineering, e.g., slope stability in civil
engineering, the understanding of mineralization and mineral
diagenesis in geosciences.
Future Research
• Clay fabric so far only partially investigated, many
unknowns are awaiting for further research. For examples:
• (1) The clay fabric in the suspension, and at the interface
between suspended and surface sediments.
• (2) The relation of clay fabric to bulk and geotechnical
properties of soils/sediments.
• (3) The relationship between clay fabric and different
environments,
• (4) The mechanism of the formation and transformation of
clay fabric though a few models has been proposed by
previous researchers.
• (5) The role of clay fabric on the surface of different rocks.
• (6) The interface between clay fabric and bioshpere.
References
Many figures and micrographs present herewith were taken from the
following books, papers cited in those books:
(1) W.;A. Chiou, 1981, Clay Fabric of Gassy Submarine Sediments:
Ph.D. Dissertation, Texas A&M University, College Station, Texas.
(2) Bennett, R. H. and M. H. Hulbert, 1986, Clay Microstructure,
International Human Resources Development Corp.
(3) Bennett, R. H., W. R. Bryant and M. H. Hulbert, 1991,
Microstructure of Fine-Grained Sediments, From Mud to Shale,
Springer-Verlag.
(4) Deep Sea Drilling Report, Leg, 488, 1981(?).
Muchas Gracias
Thank You