MINERALOGY OF THE PLAYA CLAYS AT THE PANTEX …
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MINERALOGY OF THE PLAYA CLAYS AT THE PANTEX PLANT, AMARILLO, TEXAS by KENNETH R. MARS, B.S. A THESIS IN GEOSCIENCE Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved August, 1996 ^ ^ — ^ ^
Transcript of MINERALOGY OF THE PLAYA CLAYS AT THE PANTEX …
MINERALOGY OF THE PLAYA CLAYS AT
THE PANTEX PLANT, AMARILLO, TEXAS
by
KENNETH R. MARS, B.S.
A THESIS
IN
GEOSCIENCE
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
August, 1996
^ ^ — ^ ^
f^-K- yD7 3>
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ACKNOWLEDGMENTS
I want to thank Dr. Necip Giiven for the many opportunities that he has given me
as an undergraduate and as a graduate student. Dr. Giiven has allowed me to leam and
explore the world in which we live. I want to pay a special gratitude to the members of
my committee: Dr. B. L. Allen, Dr. Tom Lehman, Dr. Kenneth Rainwater, and Dr. C. C.
Reeves, Jr. Dr. Lehman has challenged me to excel in all that I do. I hope to keep his
challenge continually before me. Dr. Rainwater, Dr. Allen and Dr. Reeves have guided
this research with typical excellence. Barbara Graham and Kaylyn Dowdy assisted with a
myriad of details and deadlines. Without their friendship, this thesis would not have been
completed within the established goals set two years ago.
I also want to thank the following scientists at the Bureau of Economic Geology
for the core needed to perform this study: Tom Gustavson, Susan Hovorka, Bill MuUican,
and Bridgette Scanlon.
I also want to go on record as saying that my family, Edna Mars, Donna and Fain
Smith, and Gwenda Mars should be listed as co-authors. I love you all very much.
It gives me the greatest joy to express love and gratitude to my new fiancee,
Elizabeth Victoria Upton. I met her at Texas Tech and now I have the privilege to leave
with her as my future wife. She provided love that was certainly unexpected and
undeserved.
Finally, I want to thank my church for their prayers and love. My Lord and Savior
Jesus Christ receives the highest praise and gratitude for His grace and love.
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TABLE OF CONTENTS
ACKNOWLEDGMENTS u
LIST OF TABLES VI
LIST OF FIGURES vn
CHAPTER
C^JTRODUCTION
Problem Statement 1
Objectives 2
Approach 2
Study Area 3
n. REGIONAL GEOLOGY 5
Introduction 5
Ogallala Formation (Tertiary) 5
Blackwater Draw Formation (Quaternary) 8
m. PLAYA BASINS 13
Introduction 13
Basin Formation 13
Proposed Models for the Origin of Play a Basins 13
Dissolution, Piping, and Eluviation 17
Salt Dissolution and Subsidence 21
Deflation 27
HI
r Animal Activity
Conclusions
V.
Recharge
Introduction
Evidence for Recharge
IV. METHODS OF INVESTIGATIONS
Sample Collection
X-ray Diffraction
Bulk Powder XRD
Clay XRD
Semi-Quantitative Mineral Analysis
Cation Exchange Capacity
Electron Microscopy
Elemental Analysis
RESULTS AND DISCUSSION
Sample Locations
Introduction
Vance #3
Sevenmile Basin #2
TDCJ #28
Wink #12
Play as 2, 3, and 5
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IV
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X-ray Diffraction
Bulk XRD
Clay XRD
Semi-quantitative Analysis
Cation Exchange Capacity
Electron Microscopy and Elemental Analysis
Applications of this Research
VI. CONCLUSIONS
BIBLIOGRAPHY
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LIST OF TABLES
3.1. Generalized characteristics of the different types of lake basins on the Southem High Plains (Reeves, 1990).
5.1 Hollow stem auger core information for play a studies (modified from Hovorka, 1995).
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5.2 Percentage by weight of coarse particles (>2p,m) and clay fractions (<2|Lim) for samples taken from Sevenmile Basin, TDCJ, Vance and Wink. 47
5.3 Percentage by weight of coarse particles (>2|im) and clay fractions (<2fim) for samples taken from Play as 2, 3, and 5.
5.4 Mineralogy of Sevenmile Basin, TDCJ, Vance, and Wink.
5.5 Mineralogy of Play as 2, 3, and 5.
5.6 Average cation exchange capacity values for samples taken from Sevenmile Basin, TDCJ, Vance, and Wink.
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5.7 Average cation exchange capacity values for samples taken from Play as 2, 3, and 5.
5.8 Table of smectite chemical formulae used in elemental analysis in Figure 5.19.
5.9 Table of chemical formulae for mica particles analyzed by EDS.
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VI
LIST OF FIGURES
1.1 Location of study area.
2.1 Distribution and water-table map of the Ogallala Formation.
2.2 Grainsize distribution of the Blackwater Draw Formation.
2.3 Generalized diagram of the soil stratigraphy from the Blackwater Draw Formation.
3.1 Three stages of playa basin on the Southem High Plains.
3.2 Playa basin model proposed by Gustavson et al (1995).
3.3 Playa basin model proposed by Reeves (1990).
3.4 Core showing dissolution in cemented sandstone of the Ogallala Formation.
3.5 Location of Lake McConnell and an unnamed playa lake.
3.6 Topographic map and stmctural cross section of Lake McConnell.
3.7 Topographic map of a part of a large playa 4.2 miles south of Pampa, Texas.
3.8 Interpreted reflection data showing the subsurface of the bedrock beneath Sevenmile Basin.
3.9 Topographic map of playa basins and aeolian dunes.
3.10 Map showing changes in potentiometric map of the Ogallala aquifer.
3.11 Plot of isotopic composition of precipitation and ground-water on the Southem High Plains.
3.12 Histogram of estimated recharge to the Ogallala aquifer.
5.1 Vance playa basin topographic map showing well locations.
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5.2 Cross section E-E' of Vance playa basin with sample location.
5.3 Sevenmile Basin topographic map showing well location.
5.4 Cross section F-F' of Sevenmile Basin with sample location.
5.5 Topographic map of TDCJ showing well location.
5.6 Cross section A-A' of TDCJ showing sample location.
5.7 Topographic map of Wink playa basin showing well location.
5.8 Cross section D-D'of Wink basin showing sample location.
5.9 Topographic map of Playa 5.
5.10 Cross section A-A' of Playa 5.
5.11 Typical bulk powder diffractogram for basins studied.
5.12 Bulk X-ray diffractogram of Sevenmile Basin.
5.13 Oriented diffractograms of clays from basins adjacent to Pantex.
5.14 Oriented diffractograms of clays from Pantex.
5.15 TEM of representative fine cluster of smectite flakes from Playa 5.
5.16 TEM of representative cluster of fine illite particles from Playa 2.
5.17 TEM of a well developed smectite from Playa 3.
5.18 X-ray spectra of smectite in Figure 5.17.
5.19 Elemental analysis of smectites from playa basins.
5.20 TEM of Fe-rich beidellite from Playa 3 showing a less developed smectite morphology.
5.21 X-ray spectra of smectite in Figure 5.20.
5.22 TEM of several plates of muscovite from Playa 2 stacked upon each other.
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5.23 X-ray spectra of muscovite in Figure 5.22.
5.24 TEM of mica from Sevenmile Basin.
5.25 X-ray spectra of mica in Figure 5.24.
5.26 TEM of cluster of minute illite from Playa 2 particles suggesting mineral instability.
5.27 X-ray spectra of particles in Figure 5.26.
5.28 TEM of weathered illite with a morphology similar to smectite from Playa 2.
5.29 X-ray spectra of particle from Playa 2 in Figure 5.28.
5.30 TEM of Fe-rich beidellite taken from Wink.
5.31 X-ray spectra of smectite in Figure 5.30.
5.32 TEM of well developed pseudo hexagonal plates of kaolinite from Playa 2.
5.33 X-ray spectra of kaolinite in Figure 5.32.
5.34 STEM of a "cracked" kaolinite particle from Playa 2.
5.35 X-ray spectra of kaolinite in Figure 5.34.
5.36 STEM of kaolinite and illite particles from TDCJ.
5.37 X-ray spectra of illite particle in Figure 5.36.
5.38 X-ray spectra of kaolinite in Figure 5.36.
5.39 TEM of sepiolite/palygorskite from Playa 5.
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CHAPTER I
INTRODUCTION
Problem Statement
The Southem High Plains of Texas contains approximately 20,000 small
ephemeral lake basins called playas. Recentiy, these playas have received considerable
attention due to the realization that focused recharge to the Ogallala Aquifer can occur
through these basins (Wood and Osterkamp, 1984, 1987; Scanlon et al., 1994; Wood et
al., 1996).
The Pantex Plant, located 16 miles northeast of Amarillo, Texas, in Carson
County, has five playa lakes on property owned or leased by the Department of Energy.
Potential contamination of the Ogallala Aquifer from Pantex has created much concem.
Measurable contamination has been detected in the soils underlying the Plant (Laun,
1995).
A sufficient knowledge of soil properties in playa basins is necessary to properly
characterize the potential of contamination. Playa basins are a major focus of surface
mnoff on the Southem High Plains. Playa basins have a distinctive surface soil, termed
the Randall soil series (USDA-SCS unpublished material, 1978). Randall soils are
defined as fine, montmorillonitic, thermic typic Halplustert. Playa basins collect mn-off
from agricultural fields, roads, pavement and other man-made stmctures that can be
sources of contamination. Mineralogy influences factors such as recharge and
contaminant attenuation through these basins.
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Objectives
The objectives of this thesis are the following: (1) define the Randall soil
mineralogy with emphasis placed upon clays, (2) define the effects of these clays on
recharge, (3) discuss the role clays have on lake basin formation, and (4) at least
qualitatively, discuss the role clays have on contaminant attenuation to the Ogallala
Aquifer. The mineralogical description of playa basin soils given in this thesis will aid
future investigators in defining the role playa basins have on regional hydrology on the
Southem High Plains.
Approach
Cores from seven playa basins were sampled for this study. Cores were taken
from Playas 2 and 3 by the Bureau of Economic Geology on January 13 and 14, 1995.
Samples from Playas 2 and 3 were taken on site as the core was collected. The cores
from Sevenmile Basin, Texas Department of Criminal Justice (TDCJ), Vance, and Wink
were taken by the Bureau of Economic Geology during 1992 and 1993. Sampling of
Sevenmile Basin, TDCJ, Vance, and Wink, for this study was conducted at the Bureau of
Economic Geology in Austin, January, 1995. Samples were taken from areas in the cores
that contained thicker sections of lacustrine deposits. In addition to lacustrine sections.
sandy regions were sampled in order to compare mineralogy. Appropriate chemical, X-
ray and electron microscopy techniques were chosen in order to describe the mineralogy.
Study Area
Seven playa lake basins located on the Southem High Plains of Texas were
selected for this study. The seven basins are: Playas 2, 3, and 5 located on the Pantex
Plant. Sevenmile Basin, TDCJ, Vance, and Wink basins are adjacent to the Pantex Plant.
Figure 1.1 illustrates the location of each basin of interest.
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QAa63e2c
Figure 1.1. Locatign of study area. The basins of interest (marked by an arrow) are: playas 2, 3, and 5, on the Pantex plant, and Sevenmile Basin, Texas Department of Criminal Justice (TDCJ), Vance, and Wink (modified from Hovorka, 1995).
CHAPTER n
REGIONAL GEOLOGY
Introduction
The Southern High Plains of western Texas and eastern New Mexico is an area
approximately 30,000 square miles in extent bounded by the valleys of the Pecos River
on the west, the Canadian River on the north, and the Red, Brazos, and Colorado rivers
on the east. The average slope of the Southem High Plains is 8 to 10 feet per mile toward
the southeast (Reeves, 1970). The surface of the Southem High Plains is underlain by the
Ogallala Formation (Miocene - Pliocene) and Blackwater Draw Formation (Quatemary).
The Quatemary Blackwater Draw Formation unconformably overlies the Ogallala
Formation. Playa lake basins (discussed in Chapter III) are the major geomorphic
features developed on the surface of the Blackwater Draw Formation.
Ogallala Formation (Tertiary)
The Tertiary Ogallala Formation (Figure 2.1) of the Southem High Plains
unconformably overlies Permian, Triassic, and Cretaceous strata. Contained in the
Ogallala Formation is the economically important Ogallala Aquifer and several perched
aquifers. The flow of water in the aquifer is to the southeast as shown by Figure 2.1. The
direction of flow is controlled by the regional dip described by Reeves (1970).
Seni (1980) studied the Ogallala Formation and argued that it represents a series
of humid alluvial fan systems originating in the eastem Rocky Mountains. Three major
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Figure 2.1. Distribution and water-table-surface map of the Ogallala Formation and Ogallala Aquifer (from Gutentag and Weeks, 1980).
fan lobes were described by Seni (1980). All three lobes were described as displaying a
downdip decrease in thickness, net sand and gravel content, and percentage of sand and
gravel. Palleovalleys, created by early Tertiary erosion and dissolution of Permian
evaporite minerals, were stated as influencing Ogallala deposition.
Reeves (1984), using field observations and thousands of drillers' logs, concludes
that the uppermost Ogallala of the Southem High Plains consists of four coalescent fans
overlain by uppermost aeolian sands. Ogallala climate progressively deteriorated,
culminating in formation of the Ogallala's "caprock" caliche (Reeves, 1996). Winkler
(1985,1987) and Gustavson and Winkler (1990) all propose a semi-arid climatic setting
during Ogallala deposition as opposed to the humid environment proposed by Seni
(1980).
Recently, studies have concluded that the Ogallala Formation does not consist of
coalescing fans (Gustavson and Winkler, 1987, 1990; Winkler, 1990). Two distinct
deposits are seen in the Ogallala formation. The lowermost section consists of fluvial
conglomerate and sandstone deposits. The uppermost section, overlying the fluvial
deposits, consists of aeolian siltstones and clay deposits. Valleys and uplands created by
erosion during the early Tertiary were filled and buried during Ogallala deposition
(Gustavson and Winkler, 1990).
Gustavson and Holliday (1990) state that the topography of the mid-Tertiary
erosional surface controls the grainsize of the Ogallala Formation. The valleys contain
braided, high-energy, ephemeral stream deposits derived from the Rocky Mountains.
Ogallala streams were later diverted, presumably due to the formation of the Canadian
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and Pecos rivers. Fluvial deposits did not develop over the valley walls suggesting that
tme coalescing "fans" did not form. The fluvial deposits and upland areas were then
overlain with aeolian deposits derived from the newly formed Pecos and Canadian
valleys. With aeolian deposits covering the paleo-uplands, a depositional model with
fluvial deposits confined to valleys was suggested as a more plausible explanation of the
Ogallala Formation.
Reeves (1972), Seni (1980), Gustavson and Holliday (1985), and Gustavson and
Winkler (1990), propose depositional systems that indicate a general upward-fining
texture in the Ogallala Formation. These textures most likely have a significant influence
on spatial distribution of porosity and permeability in the Ogallala aquifer (Nativ, 1988).
The caprock caliche, capping the Ogallala Formation, is a pedogenic carbonate
horizon. Stone (1985) stated that caliche develops from pedogenic processes, ground
water precipitation, or a combination of both. Commonly thought of as an impermeable
barrier to ground-water flow and recharge (Knowles et al., 1984), caliche has been found
to fracture and dissolve allowing some recharge (Reeves, 1976; Wood and Osterkamp,
1984; and Stone, 1985).
Blackwater Draw Formation (Quatemary)
The dominant Quatemary deposits on the Southem High Plains (Figure 2.2) is the
Blackwater Draw Formation, described by Reeves (1976). The Blackwater Draw
Formation consists of aeolian sediments covering an area greater than 100,000 km . The
source area for sediments of the Blackwater Draw Formation is thought to have been the
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Figure 2.2. Grainsize distribution of the Blackwater Draw Formation showing progressive fining of surface soils to the northeast (from Holliday, 1990).
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Pecos River Valley. Evidence for this is found in the progressive fining of surface soils
toward the northeast away from the river valley. Poorly developed drainage on the
Southem High Plains is a result of underlying Ogallala topography and regional
southeasterly slope (Reeves, 1979; Gustavson et al., 1980; Gustavson and Finley, 1985).
Frye and Leonard (1957,1965) first described the Quatemary aeolian sands of the
High Plains using the term "cover sands." The authors concluded that these deposits are
of Illinoian age. Frye and Leonard considered the sediments to be aeolian with a source
area in the Pecos River Valley. Recognizing a well developed surficial soil horizon, Frye
and Leonard (1964,1965) determined the soil to be a "Sangamon Soil." Reeves (1976)
stated that the term "Sangamon Soil" should not be applied, because many periods of soil
development are evident in these deposits.
Several other authors have noted the well developed buried soils in the
Blackwater Draw Formation (Allen and Goss, 1974; Gustavson and Holliday, 1985;
Holliday, 1988). Holliday (1990) described four soils at the type location (Figure 2.3).
The soils were deposited episodically throughout the Pleistocene (Patterson et al., 1988;
Holliday, 1988). Elsewhere, Holliday (1990) recognized as many as seven soil horizons
in the Blackwater Draw Formation, including the surficial soil. The soil horizons are
aggradational sequences of aeolian sand, silt, and clay. The age of the Blackwater Draw
Formation spans an age of at least 1.4 Ma based upon dating techniques performed by
Holliday (1989).
Gustavson and Holliday (1985), Holliday (1990), and Gustavson et al. (1991) give
very similar depositional models of the Blackwater Draw Formation. The deposition of
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Bloekwoitr Orow /"/» type section
ill
Oii
9. i
A
Bt
Bk
Btbl
5YR 3/4
SYR 3/6 SCL pr
7.5YR 5/8
L m
2 5YR3/5 SCU pt
Bfkbl icV^Y^ 2.5YR3/6 SCL Ob Btb2
ill i! 1 ;
111 9-
10
; ' i
Btb3 5YR 5/8
SCL pr
r,., u , 5YR9/1 Brkb3 L m
Bfb4 5 Y R 4 / 8
SCL pr
Kmb4 Ogallala Fm.
(Mio-Plioccnc)
If-1
v.?
f{J??Bkbl BfkbZ i
sJ
lit SS5
ii '/. B fan CO profile obove K Is eroded
SYR 8/4 • SiL m SYR 5/6 SCL Ob
SYR 8/2 L m
SYR 8 /3 SCL Ob
SYR 8/4 SIL m
•A ABB
K
Btkbl
Kb2
Guoje Ash I 4 my
Btkbs^;"^'^ SCL pr
Kmb3 Blorfco Fm. (Pliocene)
Tu/e Bosin
' I I
!i! 4J
A
Bt Btk
Btbl
ggBkbl
75YR 4/6 StC pr
75YR9/1 CL m
75YR 5/4 SIC pr
'"E?Skmb2
7 5YR6/4 Lovo Ck Ash 0.62 my.
75YRS/5 SiL pr Btb2
Tule Fm. (Pleistocene)
Busftland
>A Bt
,J^a]>"^
2-
\\ Iff.' i
Btbl 'Bkbl Btkb2 Btkb2
Btkb3
'it
.pWBtkb3
Btkb4
Btkb4 BfkbS BtbS
75YR 3/2 C Ob
I0YH3/3 C Ob
SYR 5/6 C »b
SYR 8/3 CL m 5YR4/4 C sb SYR 6/4 CL fb
SYR S/6 CL tb
7.SYR 7/3 CL Ob
5YRS/6 CL sb
7.5YR 6/4 CL m
SYR 4/4 CL m SYR 5/4 CL m
Figure 2.3. Generalized diagram of the soil stratigraphy from the Blackwater Draw Formation, Mt. Blanco Formation, Tule Basin, and Bushland. Color are Munsel; textures are SCL = sandy clay loam, L = loam, SiL = silt loam, SiC silty clay, CL = clay loam, C = clay; stmctures are pr = prismatic, ab = angular = blocky, sb = subangular blocky, m = massive (from Holliday, 1990). Bushland was taken from Allen and Goss (1974).
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the Blackwater Draw Formation appears to have been cyclic in nature. Each cycle
consists of three stages: aeolian deposition, landscape stability and soil formation,
followed by erosion. Any or all of the three stages can occur at any time. As climate
changed, cyclic stages would change in such a manner that one process would
predominate throughout the area. A cycle would most likely start with aeolian
sedimentation. Sedimentation slows while erosion remains minimal. During this time,
land surface stability and soil formation occurs. Winds then increase without deposition
in such a way that erosion dominates the area. The periods of wind erosion could have
formed the small playa lake basins. The cycle could then start over when sediment
carried by the wind is greater than the sediment taken by erosion.
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CHAPTER m
PLAYA LAKE BASINS
Introduction
Playa lake basins are the dominant geomorphic features on the surface of the
Southem High Plains of Texas and New Mexico and within Blackwater Draw Formation.
Approximately 20,000 shallow, roughly circular playa lakes are present after heavy
rainfalls (Gustavson et al., 1994). Due to the lack of an integrated drainage system on the
Southem High Plains, playa basins capture most of the overland mn-off (Reeves, 1972;
and Wood and Osterkamp, 1984).
Presently, playa basins are thought to be points of focused recharge to the Ogallala
Aquifer. Understanding playa basin formation and its effect on the Ogallala Aquifer have
attracted much scientific debate on the Southern High Plains. Hydrologic and geologic
processes have been suggested to explain the origin of these basins. However, no single
process can explain the formation of different playa basins on the Southem High Plains
(Reeves, 1990; and Gustavson et al., 1995).
Basin Formation
Proposed models for the origin of playa basins
Wood and Osterkamp (1987) propose a hydrologic model for playa basin
formation that consists of three stages (Figure 3.1). The first stage requires the creation
of a "protobasin." This can be accomplished by any means that can create a small
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•"'^mtiir
( m SANO AND CLAY
{g?q CARBONATE
pxin LOWER CONFINING LAYER
T WATER TABLE
Figure 3.1. Three stages of playa basin formation on the Southem High Plains (from Wood and Osterkamp, 1987)
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depression, for example, deflation by the wind or wallowing by bison. The underlying
deposits are porous aeolian sands that allows material, such as organic matter, into the
subsurface. The organic material is oxidized forming weak carbonic acid (H2CO3). Stage
2 is characterized by increased eluviation and development of secondary porosity by
leaching or dissolution of carbonate. Due to the increasing eluviation and porosity, the
protobasin can grow from a central location. Slope retreat allows the basin to grow
larger. Several small protobasins can join to create larger basins. Stage 3 is characterized
by development of a centripetal drainage area and by increased recharge through the floor
of the basin. Lee-side dunes can also be present at Stage 3.
Gustavson and others (1995) present a model for playa basin formation that
suggests that playa basins are stable landforms that persist throughout time (Figure 3.2).
The model employs many of the mechanisms discussed in the next section. Emphasis is
placed, however upon geomorphic and geological processes rather than hydrologic.
Hydrologic processes are viewed as secondary.
Reeves (1990) constmcts a classification system for playa basins in the Southem
High Plains. Based upon basin characteristics, three types of basins are recognized:
young-type I, mature-type II, and mature type-Ill (Table 3.1). Type I basins are small but
can grow into Type II basins if conditions are suitable (Figure 3.3). Type U basins are
larger and usually include dunes associated with deflation. A Type II basin can grow into
a Type III basin if located above fractures that can carry groundwater deep enough to
allow dissolution of underlying Permian salt beds.
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T - T j f r j - r - T - •>'±"-^ r-
i x j - i - i
- 'i xY^iff-^j^V^^^^'°P^vigni]ii^
3-±-»-£ Caprockcalcrcic (caKche)
Playa sodirricnis
Sur'acc and buried ca'cic soils in lf>c Blactfwalcr Dr.iw FoiiToiion
Small ephemeral ponds develop ort High Plaint surface as a result of conditions such as dellaiion, subsidence over salt dissolution, or dillcrential compaction. Ponding may have resulted in solution pan In caprock calcrctc.
Centripetal drainage carries runoff and sediment lo a playa lake. Periodic Hooding kills vegetation. Sediment not stabilized by vegetation may be deflated. Minimal soil CaCO, forms because Ca* * is Mushed through playa sediment by recharge. Eolian sediment accumulates as tho Blackwater Draw Formation (8V/0) on High Plains. Calcic soils develop in interplaya areas containing as much as 70 percent CaCO,.
Centripetal drainage enlarges playa basin by slope erosion. Some sediment accumulates in playa: some is deflated. Recharge through playas minimizes accumulation of CaCO,. Loess and pedogenic CnCO, accumulate on the High Plains. Variations in playa size result in inlcrbcddcd BVVO and playa sediment.
Playa basin continues to enlarge and lo accumulate sediment owing to centripetal erosion. Some sediment is deflated and lorms a lee dune. Over lime, thick calcic soils form in inierpiaya areas. Minimal CaCO, is preserved in playa sediments.
0*>M<7<
Figure 3.2. Playa basin model as proposed by Gustavson et al. (1995).
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Dissolution. Piping, and Eluviation
Carbonate dissolution is a hydrologic process that helps in the formation of playa
basins. As water enters into the subsurface through desiccation cracks, pipes, or burrows,
organic matter is carried by the water. The organic matter is oxidized in the unsaturated
zone, releasing carbon dioxide. Carbon dioxide can react with recharging ground water
Table 3.1. Generalized characteristics of the different type lake basins Southem High Plains (from Reeves,
Characteristics
Basin diameter shape
Playa diameter shape area
Topographic relief Adjacent
dune number of dunes
Caliche under basin under playa
Caliche displaced Pipes Subsidence areas Terraces Drainage TLS Numbers
Young-type I
<0.6 km round
<0.3 km round <0.07 km^ 3-5 m
no
yes locally no no no no no 1-3 m 12,634
1990). Mature-type n
0.6-1.6 km "roundish"
0.3-0.7 km round to rectangular 0.07-0.4 km^ 8-15 m
some 1
some mostly gone some yes yes yes yes 8-20 m 4,100
on the
Old-Type HI
>1.6km irregular
? elongate ? 10-30 m
yes 2-3
no no yes ? yes yes yes >20m 40
TLS = Thickness of lacustrine sediment.
*Based on counts derived from measurements of playa areas only (Parks, 1967) on the Texas part of the Southem High Plains.
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TOPOGRAPHIC LOW Caused by depositionaJ irregularities,
ungulalory action, hydrocompaction (?)
TYPE I BASIN (small playa lake basins)
Lacustrine deposition, piping, eluviation, carbonate/silica dissolution causing
near-surface subsidence, occasional deflation
TYPE II BASIN (large playa lake basin with dune)
Lacustrine deposition exceeds Continued increase in size deflation, disappears by infilling and depth of basin due to of basin by eolian processes infiltration of underlying
ground water along fractures, causing concurrent salt dissolution in Permian strata
TYPE III BASIN (large salt lakes)
Lacustrine deposition
y Regional swales QA9890C
Figure 3.3. Model for playa basin growth as proposed by Reeves, (1990).
18
^^^
forming a weak carbonic acid (H2CO3). In addition, rainfall can contains weak carbonic
acid because of reaction with carbon dioxide from the atmosphere. In addition, plant
roots produce carbon dioxide as a product of respiration producing carbonic acid.
Carbonates, such as those in the caprock caliche, can be dissolved by the weak acid.
Decaying vegetation serves as a continual source of organic matter that can be oxidized to
produced carbonic acid (Wood and Osterkamp, 1984; Osterkamp and Wood, 1987).
Osterkamp and Wood (1987) argue that evidence in favor of carbonate dissolution
is extensive (Figure 3.4). The caprock caliche is absent under most playa basins, but
present beneath the interplaya areas (Reeves, 1971; Finley and Gustavson, 1971;
Gustavson et al., 1994).
Piping is the movement of suspended material into the subsurface. A pipe can
begin as a desiccation crack, animal burrow, or blow-out produced by aeolian deflation.
With time and prolonged exposure to water flux, pipes can enlarge substantially. Reeves
(1990) recognized that pipes can begin as small holes and then enlarge 30 to 40 cm in
diameter. Osterkamp and Wood (1987) and Wood and Osterkamp (1987) note several
examples of piping around playa basins and document a study of artificial recharge from
a water-spreading basin near Lubbock. The result was the opening of pipes, created by
recharging waters, that extended 20 m below the basin.
As a result of dissolution and piping, eluviation is maintained throughout the
formation of a playa basin. Lehman and Hauser (1970) estimated that suspended solids in
playa waters range from 400 to 1000 mg/1. At this concentration, many young small
basins should fill with sediment. Observations in the field, however, show that young
19
-A
¥
Figure 3.4. Core showing dissolution in cemented sandstone of the Ogallala Formation (from Osterkamp and Wood, 1987).
20
yt^
basins are growing larger and not filling with sediments (Osterkamp and Wood, 1987).
Goss and others (1973) used clays tagged with Cs to determine the extent of suspended
sediment movement in playa basins. After applying the tagged clay to the basin, core
134 134/ samples were taken and analyzed for Cs. Clay with Cs was found two feet below
the surface of the basin floor.
Osterkamp and Wood (1987) noted the present of illuvial clay in the Blackwater
Draw Formation beneath the Gentry playa basin near Lubbock, Texas. This was
interpreted to be evidence of eluviation. Gustavson et al. (1994) argue that illuvial clay is
ubiquitous in the Blackwater Draw Formation and that concentrations of illuvial clay are
not higher under the playa basins. No evidence of filled pipes of filled dissolution voids
was recognized by Gustavson et al. (1994).
Salt Dissolution and Subsidence
Dissolution of Permian salt is a phenomenon recognized as early as 1901 by W.
D. Johnson. Adams (1963), Jordan and Vosberg (1963), and Johnson (1976) all
attributed subsurface structures to the dissolution of buried evaporite minerals.
Gustavson et al. (1986) attributed the growth of the Canadian River valley as a result of
salt dissolution. The solute load of the Canadian River reaches 3000 ppm (United States
Geological Survey, 1969-1982). In addition, the United States Bureau of Reclamation
(1979) estimated that >55,000 metric tons of sodium chloride are carried by the Canadian
River into Lake Meredith. These results confirm that salt dissolution is active and may
give rise to subsidence.
21
y
Gustavson et al. (1980) investigated the possibility of dissolution of Permian
evaporite minerals and subsidence as being mechanisms for playa basin formation. The
authors studied Lake McConnell, which lies 5.5 miles west of Pampa, Texas, and an
unnamed playa located 6.8 miles south of Pampa, Texas (Figure 3.5). Stmcture-contour
maps were constmcted for both playas (Figures 3.6 and 3.7). The maps indicate
depressions in the Blaine Formation beneath the basins. Beneath Lake McConnell, 160
feet of salt has been lost through dissolution. The data from the unnamed playa were not
as complete, but the authors interpreted dissolution as the cause for subsidence.
Gustavson et al. (1980) concluded that insufficient evidence was available at the time to
determine which occurred first, the basin followed by dissolution, or dissolution followed
by collapse to form the basin.
Using shallow seismic data from Sevenmile Basin located 16 miles northwest of
Amarillo on U.S. Highway 60, Paine (1994) studied the role of subsidence in the basin's
origin (see Figure 5.3 for diagram of the basin). Paine concluded that the surface
topography of the basin followed the subsurface stmcture of the bedrock (Figure 3.8).
Three possible explanations were provided: (1) Ogallala and Blackwater Draw
sedimentation filled a previously existing erosional feature, (2) sedimentation filled an
existing subsidence basin with no subsidence during Ogallala and Blackwater Draw
deposition, and (3) sedimentation filled an existing subsidence basin with subsidence
continuing during Ogallala and Blackwater Draw deposition. The first explanation was
rejected due to the circular nature of the basin. Seismic reflections within the
Permian/Triassic bedrock dip toward the center of the basin rather than following the
22
w
O K L A H O M A
uCTilLTfltX..^;j7Sj' ^^.^JjPSCOMB^..^—'
• pt«f« >exxi' " i * ' • B'lOCTirt plo;« > e 0 0 0 ' i ' « ) « 0 PoyQ with crgtt »«0«n
, Q L O T * tok* bovni
/ ^ ^ Limit of octi.t 10(1 anoAjien.
• StOlilt ioi led OrcO
?. ,(», Phoiofl'oph locoi.cn
Figure 3.5. Location of Lake McConnell and the unnamed playa lake. Playa locations marked with arrows (modified from Gustavson et al., 1980).
23
^ ^ ^ ~x
y
• 2'iSO
B
990
> O CO <
•600!
V E . - I S S AU l o ^ ore gamn>0 'Or loq>
OATuM S«a lr««l
Figure 3.6. Topographic map and stmctural cross section of Lake McConnell. A. Topographic map of the Lake McConnell playa superimposed on a stmcture-contour map on the top of the Blaine Formation. The depression on the stmcture-contour surface (heavy contour lines) underlies the playa depression. B. Stmctural cross section through the Lake McConnell playa derived from gamma-ray logs (from Gustavson et al., 1980).
24
v_ y
• Well
Conttxjr irdervol: 10 II
Structure contour inlervoUK) II
/ 1 . I 1
\ 1 ^ ^ 1
\ • V ^
l " " - ^ ^ < '
1760 \ ' \
Figure 3.7. Topographic map of a part of a large playa 4.2 miles south of Pampa, TX., superimposed on a stmcture-contour map on the top of the Blaine Formation. The topographic depression closely overlies the stmcture-contour depression (from Gustavson et al., 1980).
25
^
y
(s) auj i ; XBM-GMJL
OS O N
C
o ,1-1
o o U I
0)
J3
Uf
4-1
o
c/3
o
CO
X) 3 C/3
(U -G -t—>
c •? o
4—>
CJ
-a c
_o 4—>
o
2^ -o (U
4—>
0)
<u
00
3
26
y
regional dip. The existence of Sevenmile Basin was interpreted by Paine (1994) as
evidence for subsidence induced by dissolution during Ogallala and Blackwater Draw
deposition.
Havens (1966) and Gustavson et al. (1995) also present data that suggests that
some playa basins do not form due to dissolution-induced subsidence. The evidence was
based upon the observations that the depth to Permian salt across the Palo Duro Basin
increases from 200 meters in the north to 1000 meters in the south. The loss of salt
decreases from north to south. Gustavson et al. (1995) argue that if salt dissolution and
subsidence are the main factors influencing playa basin growth, detectable changes in
basin characteristics should be seen. None were found in their observations.
Deflation
Deflation is a mechanism that has been used to explain the origin of playa basins
for many years (Gilbert, 1895; Evans and Meade, 1945; Judson, 1950; Reeves, 1966,
1971). The Blackwater Draw and Ogallala formations contain thick sequences of aeolian
deposits. If sediment was deposited by aeolian transport, the same sediment can be lifted
up and redeposited some other place by the same process. The probability of aeolian
deflation on the Southern High Plains is the prominent argument of Gustavson et al.
(1995), who also hold to the idea that geomorphic (aeolian) processes are the primary
mechanism of playa basin formation. Conversely, hydrologic processes such as
eluviation, piping, and subsidence are considered secondary.
27
/
Several authors have noted that aeolian dunes are associated with many large
playa basins on the Southem High Plains (Evans and Meade, 1945; Judson, 1950;
Reeves, 1966,1971,1972). These authors also noted that many of the smaller playa basins
do not have aeolian dunes (Figure 3.9). Gustavson et al. (1995) explain the lack of dunes
in the following way: (1) aeolian sediments did not accumulate as recognizable
landforms, (2) dunes are not high enough to intersect a topographic contour, and (3)
intemal erosion into the playa basin consumed the dunes. Generally, larger basins have
well-developed crescentic dunes while the smaller playa basins do not (Reeves, 1972).
Mitchell et al. (1974) did state that the Randall soils in the playa basins can be subjected
to substantial deflation increasing the possibility of dune formation. The Southem High
Plains is obviously an area of strong winds. Deflation is a likely mechanism that can
affect the morphology of playa basins.
Animal activity
Animal activity has been presented as a means of creating playa basins as early as
Gilbert (1895). Reeves (1990) and Gustavson et al. (1995) have observed herds of cattle
grazing in muddy ponds. Mud covers the legs of the animals as they leave the pond.
Substantial sediment can be removed if this process occurs over many years with many
herds of cattie and bison. Reeves (1990) and Gustavson et al. (1995) have also observed
that cattie and other animals can break up soil cmsts and desiccation cracks. As the
sediment is pulverized, deflation becomes a very likely mechanism for sediment
28
w
Figure 3.9. Topographic map of playa basins and aeolian dunes. Topographic map is part of the U.S. Geological Survey Olton, Texas, 7.5-minute quadrangle. Dunes are marked by an arrow (modified from Gustavson et al., 1995).
29
y. vy- ~x
transport. Wood et al. (1996) have observed prairie dog holes commonly found on the
margins near playa basins. The authors conclude that these large burrows aid eluviation.
Conclusions
Three models have been presented to explain the origin of the numerous playa
lake basins on the Southem High Plains of Texas and New Mexico. All three models
employ the processes previously discussed. The models differ in the degree of
importance placed on different processes. The strengths and weaknesses of each model
are discussed below.
Osterkamp and Wood (1987) and Wood and Osterkamp (1987) present a model
largely based upon hydrology and water chemistry (Figure 3.1). Wood and Osterkamp
(1987) state: "Basins of the Southem High Plains, Texas and New Mexico, develop
mainly by micropiping and solution rather than by aeolian processes" (p. 229). The
authors do take into account increasing rainfall from west to east on the Southem High
Plains. Basin density also increases from west to east. In addition, soil mineralogy is
taken into account when discussing basin formation. Clays decrease permeability at the
center of the basin floor forcing recharge through the annulus. As the basin dries, the clay
material can be blown out forming lee-side dunes. In spite of their mention of lee-side
dunes, little attention is given to aeolian processes and salt dissolution-induced
subsidence. More attention should be paid to subsurface geology and surface geomorphic
processes.
A playa basin model (Figure 3.2) based upon aeolian processes is presented by
Gustavson et al. (1995). Gustavson et al. (1995) state, "Although fluvial erosion of playa
30
basin slopes, dissolution of soil carbonate, salt dissolution, eluviation, piping, and animal
activities probably contributed to playa development, they were of secondary importance"
(p. 38). Importance is placed upon aeolian processes. The observation that the
Blackwater Draw Formation is interbedded with playa sediments gives important
information that Osterkamp and Wood (1987) and Wood and Osterkamp (1987) do not
provide. The conclusion drawn by the interbedded sediments is that playa basins were
stable landforms during the deposition of the Blackwater Draw Formation. Hydrologic
processes should receive more attention in the model, however. Playa basins do collect
overland water mn-off. Hydrologic processes would seem to have a more important role
in basin formation than presented by Gustavson et al. (1995).
Reeves (1990) presents a model (Figure 3.3 and Table 3.1) that encompasses all of
the proposed mechanisms without attempting to place importance upon any one process.
In addition, a classification system is provided that helps distinguish between different
basins. Reeves (1990) focuses on the most likely process influencing a basin at a
particular time. For example, a young type I basin may be influenced more by deflation
than piping or dissolution. As the basin grows with time, different processes such as
piping and carbonate dissolution may begin to exert more influence than the previous
process. Type II basins commonly have dunes associated with their growth. Type III
basins are characterized by well-developed dunes and may also be associated with
Permian salt dissolution. This approach avoids trying to place a greater importance upon
hydrology, geomorphology, or geology over each other. All three are presented as being
important to the growth of playa basins.
31
Recharge
Introduction
Understanding the sources of recharge to the Ogallala Aquifer is vital to the
Southern High Plains. Since the 1940's, the watertable in the Ogallala Aquifer beneath
the Southern High Plains has been lowered due to extensive agricultural irrigation (Figure
3.10). If proper utilization and protection of the aquifer are to occur, defining the factors
affecting recharge is necessary.
Early studies (Theis, 1937; White et al., 1946; Cronin, 1964) concluded that
recharge to the Ogallala was not through playa basins. The caliche underlying the
Southem High Plains was thought to be impermeable, preventing any significant
recharge. In addition, clay-rich soils in the playa basins have low permeability. The
presence of this clay was thought to reduce recharge through the basin floors (Harris et
al., 1972; Allen etal., 1972).
Evidence for Recharge
Several studies using chloride chemical data have been conducted in order to
determine the amount of recharge that occurs through playa basins (Wood and
Osterkamp, 1984,1987; Scanlon et al., 1994; Stone, 1990; Wood et al., 1996).
Low chloride concentrations in the playa soils tend to be the strongest line of evidence for
focused recharge through playa basins. Chloride is chemically conservative, allowing it
to be used as an ideal tracer of water movement. Chloride mass balance can be used if it
is assumed that the source of chloride is precipitation and dry fallout. Chloride
32
I04»
EXPLANATION
CD
f \ \ J Riso mo'e then 10
^ise lo 10 or dcclino lo -10
'-•:-:-:-j Otc'-nt - lO lo - 5 0
[ • • ] Decline more thon 50
0
t—
lOOmi
150 Km
0A6088
Figure 3.10. Map showing changes in potentiometric surface of the Ogallala Aquifer since the 1940's (from Nativ, 1988).
33
concentrations increase in the root zones as a result of evapotranspiration (Scanlon et al.,
1994).
Scanlon et al. (1994) compare chloride profiles of playa basins with chloride
profiles of interplaya areas in an effort to qualitatively determine the water flux into the
Ogallala Aquifer. Low chloride concentrations were found in the playa basins while the
interplaya area had relatively high concentrations. Waters that infiltrate the interplaya
soils do not move at sufficient rates to avoid evaporation. Conversely, waters in playa
basins can percolate to depths sufficient to avoid evaporation. Liquids and/or
contaminants can then travel through the unsaturated zone until the saturated zone is
encountered.
Wood and Osterkamp (1984) used chloride tracers and determined that recharge
through the playa basin is concentrated in the playa floor. As the basin migrates grows
outwardly from the center, the lacustrine clay thickens at the center and becomes thinner
at the margins. The margins contain coarser material derived from the surrounding
upland areas. Recharge is concentrated along the margins due to the decreased
permeability caused by the thickening clay at the center (Wood and Osterkamp, 1984).
Stone (1990) compared chloride concentrations of playa basins with the interplaya area in
eastem New Mexico and obtained similar results.
In order to confirm playa basin recharge through independent methods, isotopic
compositions of groundwater have been investigated (Nativ, 1988; Nativ and Riggio,
1990; Wood and Sanford, 1994). Nativ (1988) stated two possible recharge mechanisms.
If recharge to the Ogallala Aquifer is diffuse over a regional area, the groundwater should
34
be isotopically enriched in 5D and 6'^0 relative to precipitation. If recharge is focused in
playa basins, ground-water should remain isotopically similar to precipitation. Nativ
(1988) found that ground-water 6D and 6^^0 values are similar to precipitation values
found on the Southern High Plains (Figure 3.11). The isotopic values were slightly
enriched, leading to the conclusion that some evaporation had occurred. Wood and
Sanford (1994), Nativ (1988), and Nativ and Riggio (1990) found ground-water beneath
the Southern High Plains enriched with tritium. Tritium could only be introduced into the
ground-water since atmospheric thermonuclear testing in the 1950's and 1960's (Wood
and Sanford, 1994).
As a result of these various techniques used to estimate recharge rates in to the
Ogallala Aquifer, values tend to differ greatly. Assumptions that are made include the
sources of chloride and tritium. The role that playa basins and interplaya areas have on
recharge is not completely understood. The complex stratigraphic, geomorphic, and
hydrologic settings on the Southern High Plains leads to great differences in calculated
recharge rates.
The literature is extensive with regard to various studies of basin recharge. It is
not the purpose of this thesis to review the voluminous studies. Mullican et al. (1995)
reviewed and compiled the literature on playa basin recharge. Readers are referred to
their study for more information. Figure 3.12 illustrates the various estimates on recharge
to the Ogallala aquifer.
Mineralogy is a factor that has not been widely discussed in studies of the factors
affecting basin formation or rates of recharge through the basins. It is the goal of this
35
thesis to add this information to the geologic and hydrologic literature regarding playa
basins.
36
(a) 1 20-
0 -
20-
EXPLANATION
a o
+
X
A
AmofiHo
LubbocK
Midlond
Clovis
Poducoh
-40 -
-60-
Q to
-80
-100-
-120-
-140
-160
-23
Ronge of ground-water volues in the High Ploins os shown in graph below
j O : 8 J " o n o
^^t^'^"^ EXPLANATION
o Ogollolo (north)
Ogollolo (south)
Crttoceous
Tr io is ic
Permian
Ployo woter
Plojra well
Saline lake
T 1 i 1 1 r 8 - 6 -4
S'80(V..)
1^
-20 - I — •16 -12
~r T 0
S'SQC/oo)
0A6e98
Figure 3.11. Plots of isotopic composition of (a) precipitation and (b) ground water of the Southem High Plains (from Nativ, 1988).
37
v> n > s
SS Q.
JT cn 3 O
JS n n H
— u o c C C 3 o o rr o o <8 S-
o> o) i *- -t. «o "9 V. Si'ffl en ^ c S «? 5 .c x: 8 .212
o> o o c c c "3 o o rr o o <8 S-
Q : U . . £ W Z C : a II II II II II II
• •
Q
e
0
o
• ^
O as «o
0 ...(0661) euois n
-..{066l)euo»s Q
..(BesOAUBN
^19961) sjemo pLre /estonn
0 ...(S960 >pnoor< PUB 8U01S
.(9961) HJnOSkN PuB euois
(W61) euois
....(W6l) euois
0 ..(v«6l)euots
(^96l) sjeqjo pu« SBJUOKIO
(^W6l) SJ9L80 puB seiMoux
.(r«6l)se|MOux
-..(rflai) s!}B4ed P*JB pooM
.(W6l) sflBJied ptre pooM
--..(^861) dum^eiSQ puB pooM
.(W6i) dure^eiso puB pooM
(Wei) BBJUBVIO pUB S IOBM
.(2861) uoBBu;Bp«u jo nsojng -STl
.(lB6l)liiJe|>)
.(6Z5l)uosujonpuB Ilea
.(EZ6l) XXJ6|S puB UMOjg
.(9961) SUBABH
,(l96l)u!UQJ0
.(1961) OuoT
-.CiCSl) Sjeiu
.(SV60.iex«Q
.(906l)PinO9
.(I06l)uosuyor
0
IT) ON ON
O
t - i
cr a
O
W ) s->
x: o D I-I
O on D
c3
o B a <- i
O C/5
CN
cn Ui
38
CHAPTER IV
METHODS OF INVESTIGATION
Sample Collection
All sediment samples used in this study were taken from cores obtained by a
hollow stem auger. Samples 0.5 to 1.0 inch thick were collected. The majority of
samples were taken from sections of thick lacustrine clay deposits. However, samples
from sandy horizons were taken for comparison. Samples from Playas 2, 3, and 5 were
collected on site. Samples from Playas 2, 3, and 5 were wet and had to be dried overnight
in an oven at 60°C. Samples from Wink, Seven Mile Basin, East Vance, and Texas
Department of Criminal Justice, were collected from cores stored at the Bureau of
Economic Geology in Austin, Texas.
X-ray Diffraction (XRD)
Bulk Powder XRD
Approximately 5 grams of sample were ground into powder by hand using a
mortar and pestie. The sample was packed into a aluminum holder and analyzed using a
Phillips X-ray diffractometer generating Cu Ka radiation. The diffractometer was
operated at 40 kV and 20 mA with a 0.2 mm receiving slit. The sample was scanned
from 2° to 65° 20 at 1° 20 per minute. The (060) reflection was used to determine the
dioctahedral («1.50A) or trioctahedral (^1.54-1.52A) nature of the clays.
39
Clay XRD
In order to obtain workable oriented clay XRD patterns, 0.3 g of whole sample
was centrifuged three times with 0.3 N CaCb. The excess salt was washed with 1%
glycerol solution until dispersion was obtained. After dispersion, the Ca-saturated
suspension was allowed to settle according to Stokes Law to achieve a <2|im fraction.
The <2|xm fraction was pipetted onto an aluminum slide and allowed to air dry. The air-
dried slide was dried for 9 hours at 60°C and then analyzed.
Semi-Quantitative Mineral Analysis
Four grams of whole sample were used to determine the total percentage of >2fim
and <2|im. The sample was suspended using 0.223% tetrasodiumpyrophosphate (TSPP).
Solutions were shaken in a 20 ml vial by a mechanical shaker and then allowed to settie
until only a suspension of <2|im could be obtained as predicted by Stokes Law. This was
repeated until the solution was clear. The <2|Lim suspension was collected in a plastic
sample container. The >2|a,m fraction was placed into a previously weighed aluminum
dish and dried at 100°C overnight. The >2|Lim fraction was allowed to cool and weighed
to determine the >2|im percentage and the <2fim percentage.
To determine the percentage of specific clay minerals, the Ca-oriented slides were
compared to standard clay oriented XRD pattems and normalized to the <2)im
percentage. The illite/smectite mixed-layers were estimated as if they were discrete
mineral particles. All calculations were estimated by referring to the standard illite.
40
The bulk powder XRD pattems were used to determine the >2|xm mineralogy.
Standard patterns of quartz, anhydrite, calcite, feldspar, and dolomite were used. Sample
peak intensities were compared to the standard peak intensities and then normalized to
the >2|im percentages.
Cation Exchange Capacity (CEC)
The <2ia,m suspensions obtained from the semi-quantitative mineral analysis were
used to determine CEC values. In order to obtain only clay CEC, organic matter was
removed using hydrogen peroxide, following the methods described by Jackson (1965).
With organic matter removed, the suspensions were allowed to air dry and then ground by
hand with a mortar and pestle. Using 0.2 to 0.5 g of clay, CEC was determined using the
method described in the USDA Handbook 60 (1954).
Electron Microscopy
Twenty milliliters of clay suspension (with organic matter removed) were
examined with transmission electron microscopy (TEM). Sample preparation began with
adding several drops of suspension into a dilute solution of tertiarybutylamine. A copper
grid mount was covered with a thin formvar film. A drop of the tertiarybutylamine
solution with clay was placed on the copper grid and allowed to air dry ovemight. The
grid was then placed in a vacuum evaporator and coated with carbon. The grid was
stored in a dessicator until analysis was performed.
41
A JEOL JEM 100-CX electron microscope was operated at 100 KeV. Energy-
dispersive analysis (EDS) of the x-ray spectra was performed by a KEVEX 8000
microanalyser. Using standard mineral K-factors and the information provided by the
EDS, a chemical formula was calculated.
Elemental Analysis
Using the data from the EDS analysis, elemental analysis can be performed to
determine the species of a particular smectite particle. The procedure for calculating
smectite formulas has been described by Sawhney and Jackson (1958): (1) the elemental
contents of all other minerals must be subtracted from the total analysis, (2) all Si is
placed in the tetrahedral sheet, (3) 22 negative charges are assumed per half unit cell (10
O atoms and two OH atoms), (4) up to one Al atoms included with Si to get four
tetrahedral atoms per half unit cell, (5) the remaining cations, usually Al " , Fe " , Mg^^ are
placed in the octahedral sheet, (6) exchangeable Ca " , Mg " , Na^, K , and H" are used to
satisfy the isomorphous substitutions. Due to the presence of K"*" in all analyses, an
interlayer K of 0.40 was used to differentiate between smectite and illite.
42
CHAPTER V
RESULTS AND DISCUSSION
Sample Locations
Introduction
Seven playa basins were selected for study in this thesis. Three playa basins are
owned of leased by the Department of Energy Pantex facility near Amarillo, Texas. The
other four playa basins were selected adjacent to Pantex (see Figure 1.1). Hollow stem
auger cores were obtained from all seven basins (Table 5.1).
Topographic maps and cross-sections for each basin were generated by the Bureau
of Economic Geology. The location of samples used in this study have been placed on
these cross-sections. A brief description is added for clarity in discussion. Only one core
each was drilled in each one of Playa basins 2 and 3, insufficient for cross-sections.
Vance #3
Two interconnected playa lakes form one playa basin (Hovorka, 1995) as shown
in Figure 5.1. Core #3 is located in the northem portion of the playa basin floor. Cross-
section E-E' illustrates the stratigraphy of the basin (Figure 5.2). Samples E3a-E3c are
Randall clay soils. E3d and E3e are a lacustrine red clay while E3f and E3g are clayey
sands. In general, clay content decreases with increasing depth (Table 5.2).
43
0 750 m
Contour interval 10 It
Borehole Paved road Unpaved road OAbS39e
Figure 5.1. Vance playa basin topographic map showing well locations. Cross section E-E' shown in figure 5.2 (from Hovorka, 1995).
44
0 6C0 (t I f 1 0 180 m
Vertical exaggeraiion > 33
PLAYA FACIES
Fine-grained lacussrine
Lacustrino-eolian sand and silt
|;:iS;|i|i§| Lacustrine clay with sand inierbeds
^ ^ ^ H Lacustrine delta
Red clay and mud
Colluvium
Lake margin
SLOPE AND UPLAND FACIES
Upland accrctiona.7 lacies
Pullman soils
Lower medium sand
Channel
8k OAeS40c
Figure 5.2. Cross section E-E' of Vance playa basin with sample locations (modified from Hovorka, 1995).
45
Sevenmile Basin #2
Sevenmile basin is the largest basin studied, suggesting an older age (Figure 5.3).
Cross-section F-F' illustrated the complex stratigraphy of this basin (Figure 5.4).
Hovorka (1995) described two thick sequences of lacustjrine deposits. All of the samples
taken from core #2 have a fairly uniform clay content which agrees with Hovorka (Table
5.2). Samples 7-2a and 7-2b are in the Randall clay soils with the remaining samples
being in older lacustrine deposits. Samples 7-2f through 7-2h (lower lacustrine sequence)
are located in an area interpreted by Hovorka (1995) as having a pedogenic overprint.
Table 5.1. Hollow stem auger core information for playa studies (modified from Hovorka, 1995).
Playa and borehole number
Playa 2 #1
Playa 3 #1
Playa 5 #18
Sevenmile Basin #2
Vance #3
TDCJ #28
Wink #12
Total depth(ft) of sampled core
51.2
53.6
41.1
53.6
61.5
63.7
52.0
Facies
basin floor
basin floor
playa
playa
playa
playa center
playa
46
Table 5.2. Percentage by weight of coarse particles (>2pm) and clay fractions (<2|im) for samples taken from Vance, Sevenmile Basin, TDCJ, and Wink.
Sample
E3a E3b E3c E3d E3e E3f . E3g E3h
7-2a 7-2b 7-2c 7-2d 7-2e 7-2f 7-2g 7-2h
T28a T28b T28c T28d T28e T28f T28g T28h
Wa Wb Wc Wd We Wf Wg Wh
Depth (ft.) % Vance Basin
1.1 8.0 15.5 24.7 34.8 40.0 50.0 61.5
>2mm
48 44 56 68 60 72 85 91
Sevenmile Basin 1.2 8.3 11.1 18.4 25.6 31.2 40.3 53.6
TDCJ 1.4 8.3 15.5 18.5 28.0 37.9 45.9 63.7
Wink Basin 1.0 7.8 11.2 18.2 23.2 31.9 47.4 52.0
40 30 44 41 40 68 47 48
39 40 36 45 42 40 50 80
44 52 55 68 72 61 60
30
% <2mm
52 56 44 32 40 28 15 9
60 70 56 59 60 32 63 52
61 60 64 55 58 60 50 20
56 48 45 32 28 39 40
70
47
0 750 m Contour inlerval tO It
V^^ Playa lake mfMii Basin lloor Kj Slope j Upland • Borehole Unpaved road Paved road OAb54ic
Figure 5.3. Sevenmile Basin topographic map showing well location. Cross section F-F' shown in figure 5.4 (from Hovorka, 1995).
48
F West
P East
(ft) (m) 7 3500-1
0 1200 It I 1 1 0 360 m
Vertical eiaggeralion i 65
> o .• 3, c g
>
Delia or channel
Slope wash-alluvium g^opg AND UPUND FACIES
1 strong peoogenic 1 11 overprint
•:;:::x'l Red clay and mud i Upland accretionary lacies
Fine sand
R
A Bk
Bt
SOILS
Pullman
Lolton, Church, and Zita
Randall clay
Buried soils
OAbS42c
Figure 5.4. Cross section F-F' of Sevenmile Basin showing sample locations (modified from Hovorka, 1995).
49
TDCJ #28
Core #28 is located in the center of the playa basin (Figure 5.5). Cross-section A-
A' illustrates the north-south stratigraphy of the basin (Figure 5.6). Hovorka (1995)
describes four lacustrine units, of which core #28 transects all four. Samples T28a
through T28e are located in the fourth and uppermost sequence. Sequence 3 is a sandy
clay from which sample T28d was obtained. Large amounts of coarse material (>2|xm)
for sample T28d coincides with Hovorka's observations (Table 5.2). Samples T28e and
T28f are located in sequence 2 while T28g is located in sequence 1. Underlying the first
sequence is a coarse sand from which sample T28h was taken . The >2|im fraction in
T28h is 80% of the total material, agreeing with Hovorka's comments.
Wink #12
Core #12 is located approximately in the center of the playa basin (Figure 5.7).
Cross-section D-D' illustrates the stratigraphy of the basin (Figure 5.8). Two samples,
Wa and Wb, are located in the Randall clay soil deposits. Sample Wc represents an older
lacustrine deposit, whereas samples Wd through Wf are located in an area of
interfingering of lacustrine and clay-aeolian deposits (Hovorka, 1995). Samples Wd and
We have a lower clay content, while Wf has a greater clay content suggesting a lacustrine
origin. The underlying reddish clay is sampled in Wg and Wh. With the exception of
Wh, clay content decreased with increasing depth.
50
0 750 m Contour interval 10 H
2600 (1 f—J Trench (no! to scale)
GPR line
• Borehole
— Paved road
— Unpoved road
I I I I I > Railroad
QAbSJSc
Figure 5.5. Topographic map of TDCJ basin. Topography from Pomroy and Abel 1:20,000 quadrangles. Cross section A-A' shown in figure 5.6 (from Hovorka, 1995).
51
PLAYA FACIES
I Fine-grained lacustrine
Lacustrine-eolian sand and silt
[lliiill;:) Lacustrine day with sand interbeds
^ ^ H Lacustrine delta complex
SLOPE AND UPLAND FACIES
^ ^ ^ Pullman and slope soils
Upland accretionary (acies
Lower medium sand
0 180 m Vertical exaggeration x 33
%"€
Bk
Channel
Intraclasts
OA6534C
Figure 5.6. Cross section of A-A' of TDCJ playa basin showing sample location (modified from Hovorka, 1995).
52
• Boret oie
Paved road
0 750 m Contour interval 10 It QAt>537c
Figure 5.7. Topographic map of Wink playa basin showing well location. Cross section D-D' shown in figure 5.8 (from Hovorka, 1995).
53
•
•
•
1 \^^ •.\
O- l -O o
Ila
o •o
0) c ^ 3 o (0
3
F •o
c ra
ra u •D 0)
CO LIJ
o < u.
I •o 0)
I
.-. o
o
o 1 -o
1 ^ 1 ^ o
(isai 8Aoqe) UOIIEASI^
UJ
o if
Q. 13 Q < LU 0 .
O _i (/)
ra C ra
tr a
•n c ra I/)
c o <u M c
ilh
< _ra a> c
•o
r> o
o TO h o
LL
ra
lal
C3)
O
01 c c ra (J
3 -O O C TO ra
1 )
0) a o
T> c ra c ra h 3
0.
£• ra
u
-o c a. 13
T3
ra
F
f, S
t _ i
ON ON
O > O
o
-a
-a o
c ' • < — >
o
'a, cd oo
C
• ^
o x: C
a M c
4—»
O
(A
o
u
3
54
Playas 2, 3, and 5
Cross-sections for Playas 2 and 3 are not available due to the lack of core. The
general pattern of fining-upward that was observed in the samples from the adjacent
basins, is also observed in Playas 2, 3, and 5 (Table 5.3). The cross-section for playa five
(Figure 5.9) is illustrated in Figure 5.10. Bore hole #18 was not used in the construction
of the cross-section. However, the thin lacustrine deposits (8.5 ft.) found in Playa 5 are
localized in the northem portion of the basin. The reason for this is unclear at this time.
X-ray Diffraction
Bulk XRD
Bulk powder XRD diffractograms for all samples are similar (Figure 5.11). The
common minerals (Tables 5.4 and 5.5) are quartz, plagioclase, and potassium feldspar
with quartz becoming more abundant with increasing depth. Only samples from
Sevenmile Basin #2 contain consistent abundance of calcite (Figure 5.12). The close
proximity of hole #2 to the upland slope may be the reason for the large amounts of
calcite. Playa 5 contains measurable calcite deeper in the basin. Playa 2 contains a
mineral whose d-spacing at 3.49A coinciding with anhydrite. Anhydrite needs an
environment that is characterized by hot soil temperatures and low moisture content. The
playa floors are neither of these. Playas 3 and 5 contain lesser amounts of anhydrite while
being absent in the basins surrounding Pantex. The presence of anhydrite is most likely
an artifact resulting from the drying of wet samples in the oven. Dolomite is present in
55
11 I 11 M Railroad
© Hollow stem auger tx>rehole
• Well OA05*6t
Figure 5.9. Topographic map of Playa 5. Cross section A-A' in Figure 5.10 (from Hovorka, 1996).
56
ON ON
OS
U I O > o
o
cd >-» cd
K, O
< I
< c o
-4—>
o (U c/5 00 C/3
O I-I
U d
3
57
Table 5.3. Percentage by weight of coarse particles (>2|im) and clay fractions (<2|Lim) for samples from Playas 2, 3, and 5.
Sample
2a
2b
2c
2d
2e
2f
2g 2h
3a
3b
3c
3d
3e
3f
3g 3h
5a
5b
5c
5d
5e
5f
5g 5h
Depth (ft.)
3.0
8.6
12.5
23.7
33.7
45.9
49.5
51.2
2.3
10.3
18.2
23.1
33.4
43.6
48.6
53.6
3.5
8.5
16.0
21.0
26.0
31.0
36.0
41.1
Playa 2
Playa 3
Playa 5
% >2|im
40
41
40
45
34
91
92
87
44
71
27
66
56
69
61
75
63
64
85
84
86
87
80
87
% <2jLim
60
59
60
55
66
9
8
13
56
29
53
34
44
31
39 25
37
36
15
16
14
13
20
13
58
O NO
o
o
O
O
•n
CO 1 ^
o
H
H O
g >
•n ct)
S" P LH
__ o
«n
CO
N
cr II a
T3
cn
J3
.2 S U I
o o
O ex.
3
O
>^ H
o 00
o
AUSMaXJSII aAUVlSH
59
Table 5.4. Mmera ogy of Sevenmile Basin, TDCJ, Vance, and Wink. (Qtz = quartz, Pla = plagioclase, K-Fel = K-feldspar, Cal = calcite, Dol = dolomite Anh = anhydrite, 111 = illite, Sme = smectite, Kao = kaolinite)
iHlElS I^epth(ft.) Qtz Pla K-Fel Cal Dol Anh 111 Sme Kao | Vance Basin
E3a E3b E3c E3d E3e E3f E3g E3h
7-2a 7-2b 7-2c 7-2d 7-2e 7-2f 7-2g 7-2h
T28a T28b T28c T28d T28e T28f T28g T28h
Wa Wb Wc Wd We Wf Wg Wh
1.1 8.0 15.5 24.7 34.8 40.0 50.0 61.5
1.2 8.3 11.1 18.4 25.6 31.2 40.3 53.6
1.4 8.3 15.5 18.5 28.0 37.9 45.9 63.7
1.0 7.8 11.2 18.2 23.2 31.9 47.4 52.0
44 33 52 48 48 63 71 70
18 18 27 27 18 43 21 26
32 34 28 40 30 36 41 65
39 45 46 45 50 56 48 27
2 7 4 5 3 .
8 7
2 4 _
13 9 9 6 14
2
»
Sevenmile Basin 1 2 3 3 1 10 3 9
4 4 4 3 7 4 3 9
1 _
3 3 1 7 1 5
TDCJ 4 -
-
2 5 -
5 6
19 9 12 8 20 7 11 9
•
2 4 _
-
-
-
-
Wink Basin 5 3 6 11 5 3 . 11 2
-
3 4 9 15 -
2 -
-
-
-
2 1 2 2
-
- _
38 41 22 17 28 15 7 4
25 34 26 27 31 14 30 24
30 37 40 30 38 44 37 13
28 24 22 15 12 17 15 32
7 7 19 12 9 10 7 5
30 31 23 28 24 17 25 25
25 17 18 17 13 10 8 7
24 20 19 15 14 19 23 34
7 8 3 3 3 3 1 -
5 6 6 4 5 2 8 3
5 6 6 8 7 6 5 -
4 4 4 2 2 3 2 5
60
Table 5.5. Mineralogy of Playas 2, 3, and 5. (Qtz = quartz, Pla = plagioclase, K-Fel = K-feldspar, Cal = calcite, Dol = dolomite, Anh = anhydrite, 111 = illite, Sme = smectite, Kao = kaolinite)
Sample
2a 2b 2c 2d 2e 2f
2g 2h
3a 3b 3c 3d 3e 3f
3g 3h
5a 5b 5c 5d 5e 5f
5g 1 5h
Depth (ft.)
3.0 8.6 12.5 23.7 33.7 45.9 49.5 51.2
2.3 10.3 18.2 23.1 33.4 43.6 48.6 53.6
3.5 8.5 16.0 21.0 26.0 31.0 36.0 41.1
Qtz
26 30 31 34 28 70 80 74
37 45 36 41 44 58 52 72
56 48 58 76 73 74 52 63
Pla
4 3 3 5 3 5 5 6
4 10 5 12 6 5 -
-
4 6 3 1 5 4 13 8
K-Fel Playa 2
7 3 2 4 -
12 3 3
Playa 3 3 14 -
9 5 6 4 3
Playa 5 3 4 7 3 4 9 12 7
Cal
1 2 -
-
1 -
-
2
-
-
-
2 1 -
-
—
-
-
16 -
1 -
2 9
Dol
-
2 -
-
-
1 -
-
-
-
-
-
-
-
-
—
-
-
1 -
-
-
1 -
Anh
1 2 3 2 1 3 3 2
-
2 6 -
-
-
5 —
-
6 -
4 3 -
-
-
Ill
33 34 28 31 37 4 3 7
30 12 24 16 24 15 20 11
17 18 6 5 6 6 9 7
Sme
23 21 27 19 24 4 4 4
22 14 25 15 17 14 16 12
18 15 8 10 7 7 10 4
Kao
4 4 5 5 5 1 1 2
4 3 4 3 3 2 3 2
2 3 1 1 1 -
1 2
61
o VO
m
. - H
o o u-1
»o • *
o "? ! •
»o r«->
o r<")
U-) CS
o cs
t r i
CT) U S o Ui
w ffl H O
nee
of c
a ep
re
- C • 4 — >
(U
o
z, c
• v>4 oo cd
PQ u
c o >
00 t ( - l o
B cd u OJQ
O 4—• o cd
J+-^ t U l . r H
-o -r
ay
X
Bul
k
U i
cd Cu
T )
3 ur; II
UH
4—> . r H
ale
CJ
II
u
artz
3 U ' II
cy > , cd C)
II
U
CN
AlISNaiNI SAIXViaH
62
minor amounts in Playas 2, 5, and Wink. The dolomite is most likely derived from the
surrounding upland area.
The basal reflection (00/) of clay minerals are absent in all patterns. This is a
result of poor crystal Unity and possibly interstratification. Also, random orientation
precludes significant 001 reflections. However, (060) reflections are present in all
patterns. The (060) values for all diffractograms are =1.50 A suggesting dioctahedral
clays. Bulk mineralogy appears to be basically the same in all samples analyzed.
Clay XRD
Oriented clay diffractograms for all samples are similar (Figures 5.13 and 5.14).
Detrital illite appears to be the dominant mineral present in all basins. However, illite is
more abundant (discussed later) and more crystalline producing better reflection peaks
than the peaks produced by the smectite. Values for CEC (discussed later) suggest more
smectite than indicated by the diffractograms. Smectite peaks are broad, suggesting
smaller poorly crystalline particles.
The diffractograms from Vance Basin are the poorest. The reason is unclear.
Kaolinite is present in all basin samples with the exceptions of E3h, T28h, and 5f.
Kaolinite is produced in acid environments (Dixon, 1989). The kaolinite is most likely
derived from the surrounding uplands and not authigenic (Allen et al., 1972).
63
-4-J
3 cci
- ^
II rN
«>
o a>
CO
C/D (U
X 4>
c cd PL^
o - * - »
ace
• ^ • ^
T3 cd 03
c: cd
-O
6 o <h <Ji >, cd o
C4-I 0
6 cd U i CD 0
•4- .»
0 cd
ffr
• *- - 0
-*-> c: <L>
0 frt 0 II
U TJ c cd
rtz,
cd - l cr II
a ^^
cd ^ ™ ^
0 c 0 c g 0 0
II U CJ
m
<L> u 3
AXISMaXKI SAIXViaM
64
o
o CN
•n
•n
^
o S S o o II
O
o ed
U II
O
B Vi H
X
ed o
C! ed
-o c ed
N
ed
.2 a
AXIS^aXMI SAIXViaH
o C4-1
o v>
B ed U I 00 o o ed
SS T3
c *c o
(L> u 3 00
65
Semi-Quantitative Analysis
In coarse fractions (>2)im) of all samples, quartz is the dominant mineral (Tables
5.4 and 5.5). Quartz, plagioclase, and potassium feldspar abundance tends to increase
with depth. This is probably a result of playa basin growth over time. As a basin grows
laterally and vertically, more run-off can be collected. Clay minerals can be carried by
the run-off waters easier than the coarser minerals, allowing more colloidal accumulation
in the deeper water farther from the shoreline. The deeper sands are likely the original
cover sands present before basin development. Calcite is not present in most playa
samples presumably due to dissolution by percolating waters.
The clay mineralogy of all basins consists of detrital illite, smectite, and kaolinite
with clay content decreasing with depth (Tables 5.4 and 5.5). Kaolinite is in all cases less
than 10% in the samples collected. The formation of kaolinite is not expected due to the
poor drainage of the Southern High Plains. Authigenic kaolinite occurs in high leaching
acidic soil environments (Dixon, 1989). Smectite peaks are broad allowing for only
conservative estimates of amounts present. Smectite generally makes up about 20 to 34%
of the sample. All smectite is dioctahedral ranging in chemistry between montmorillonite
and beidellite end-members (discussed later). There seems to be no enhancement of
particle crystallinity with depth. The amount of illite ranges from 20 to 40% of the
sample. Illite crystallinity appears to remain the same with increasing depth. As
discussed later, illite is present in many different stages of weathering and
interstratification.
66
CEC
Cation exchange capacity (CEC) of all samples was determined except for
samples 2f and 2g. Insufficient clay was available for samples 2f and 2g. With larger
percentages of illite than smectite, CEC values would be expected to be low. This is not
observed (Tables 5.6 and 5.7). CEC values generally fall in the range of 60 top 96
meq/100 grams. (Note: CEC values over 100 are suspect.) Playa 5 has the lowest values.
This is a result of the basins' low clay mineral content (Table 5.4). Note that Playa 5 has
the lowest clay content of all basins sampled. Lacustrine deposits are only 9 feet thick,
and underlain by aeolian sands of the Blackwater Draw Formation sands. E3h has the
lowest value of 33 meq/100 grams. Two possible explanations are apparent. The amount
of sample was very littie allowing error to be introduced in the procedure. Secondly,
smectite amount could be low. The former is most likely the case because E3f and Efg
have low clay content but CEC values are comparable to the more clay-rich samples.
There is no apparent difference in CEC values among the different basin samples.
EM and EDS
Electron microscopy of samples from all seven basins confirmed the previous
conclusion of poor crystallinity and fine particle sizes of smectite (Figure 5.15). Illite is
present in finer fractions (Figure 5.16) but is not as prevalent as smectite.
The smectite found in all playa basins contains interlayer potassium as revealed by
EDS analysis. The presence of potassium in smectite can be explained by (1)
interstratification of illite with the smectite, and (2) smectite is a weathering product of
67
Table 5.6. Average cation exchange capacity values for samples from Vance, Sevenmile Basin, TDCJ, and Wink.
Sample
E3a E3b E3c E3d E3e E3f E3g E3h
7-2a 7-2b 7-2c 7-2d 7-2e 7-2f 7-2g 7-2h
T28a T28b T28c T28d T28e T28f T28g T28h
Wa Wb Wc Wd We Wf Wg Wh
Depth (ft.) Average CEC
1.1 8.0 15.5 24.7 34.8 40.0 50.0 61.5
(m Vance Basin
eq/100 g)
82 82 90 93 87 79 72 33
Sevenmile Basin 1.2 8.3 11.1 18.4 25.6 31.2 40.3 53.6
1.4 8.3 15.5 18.5 28.0 37.9 45.9 63.7
1.0 7.8 11.2 18.2 23.2 31.9 47.4 52.0
TDCJ
Wink Basin
95 75 105 104 84 108 94 93
83 85 93 81 90 87 96 108
78 76 85 82 86 84 80 72
Standard Deviation (meq/100 g)
3 3 4 3 3 7 1 2
1 1 2 4 2 4 3 0
1 1 2 3 5 2 2 4
2 3 2 2 1 4 2 4
68
Table 5.7. Average cation exchange capacity values for samples from Playas 2, 3, and 5 Sample
2a 2b 2c 2d 2e 2f 2g 2h
3a 3b 3c 3d 3e 3f 3g 3h
5a 5b 5c 5d 5e 5f 5g 5h
Depth (ft.)
3.0 8.6 12.5 23.7 33.7 45.9 49.5 51.2
2.3 10.3 18.2 23.1 33.4 43.6 48.6 53.6
3.5 8.5 16.0 21.0 26.0 31.0 36.0 41.1
Average CEC
Playa
Playa
Playa
(meq/100 g) 2
3
L5
83 82 80 77 71
-
-
74
93 84 85 83 79 87 96 95
68 66 65 82 75 73 66 60
Standard Deviation (meq/100 g)
4 3 3 8 11 -
-
1
10 7 4 5 4 6 4 5
2 2 2 2 3 3 4 4
69
Figure 5.15. TEM of a representative fine cluster of smectite flakes from Playa 5 (50,000X). Bar equals 0.5|Lim.
Figure 5.16. TEM of a representative cluster of fine illite particles from Playa 2 (26,000X). Bar equals l.O^m.
70
illite. The best developed smectite particles reveal the least amount of interlayer
potassium (Figures 5.17 and 5.18). The smectite in Figure 5.17 is a montmorillonite as
revealed by elemental analysis (Figure 5.19). Smectite morphology and crystallinity
diminishes with increasing presence of potassium in the interlayer (Figures 5.20 and
5.21). This suggests that smectite may be forming as a result of illite weathering.
Detrital muscovite is present in all playa basins. Figure 5.22 shows a well
developed mica from a depth of 23.7 in Playa 2. The mica has an interlayer potassium
content of 0.98 (Figure 5.23). The crystallinity of mica flakes decreases as the interlayer
potassium is removed. Figure 5.24 shows a mica that looks more subhedral or even
anhedral than the mica in Figure 5.22. The sample in Figure 5.25 has an interlayer
potassium content of 0.86. Also noticeable are the cracks forming in the flake suggesting
mica weathering. Evidence for illite weathering is abundant throughout all playa basins
(Figure 5.26). The illite in figure 5.26 appears to have been coherent at one time. The
interlayer potassium content is 0.40 (Figure 5.27). In spite of the mica found in Playa 2 at
23.7 ft. (Figure 5.22), weathered mica/illite particles far outnumber unweathered
particles.
Upon first viewing of the particle in Figure 5.28, smectite was the interpreted
mineralogy. Smectite generally displays a "fuzzy" film morphology under the electron
microscope. EDS analysis reveals, however that an illitic composition is present with an
interlayer potassium content of 0.44 (Figure 5.29). Figures 5.30 and 5.31 show a
smectite sample with an interlayer potassium content of 0.36. This particle is very similar
to figure 5.28 because both appear "fuzzy" with no distinct edges.
71
Figure 5.17. TEM of a well developed smectite from Playa 3 (26,000X). Bar equals 1.0|Lim.
3:-'2,'i^^ l5:ESi5i^
4i£ "ount: .i$p« 1
RNk>Uindow Ritio
I n s»:s
0 HA VfaKA M M
i^ Ml) FJB NR In
R w'
Q.Q33
A'5lV
tffl in3.n ii2.eE
k
331.8D
SI ^
WBSMr'—*^
22.8580 4.179B
P9 •mm
10.233 kfV
8.6378 ^ d 8.1185 MM
K ! L L £ : : ^ H ^
• cu ^^ocU^
1
Ql __-rv
10 . : : : Ijiifgrji C
Figure 5.18. X-ray spectra of smectite in Figure 5.17. The chemical formula is Ko.o7(Si3 82Al() i8)(AIi 2iMgo.63Feo i6)Oio(OH)2nH20.
72
o o
ed c
cS CO
t—t
tq Q w m
z o rJ
S o
2 O
CN
< > H
PLA
•
m < >^
PLA
•
•n < > H
PLA
•
m u
> <
Z • - H
c/) < CQ PLI -J
r--X
* - > H l ^
rue
WIN
O D
o «o
o o
ed CA
• < - »
C4.H o
-t-t
O E ed
JS •4->
o z (/) c (/) ed
cn >» ed O .
B o tfe CO
• r H
o 0)
. r H
^ 3 a>
r O
T3 C ed
a> "5 o ;::^ ^ H
O d
-<-» c o S
o o
o >o o
o
C« J 3
c« • £ :
13 c ed
13 C a> B
W ON
i n
U i
3)
(»J+IV)/IV M0IXIS0dI\I03 TVlia3HVX30
73
Figure 5.20. TEM of Fe-rich beidellite from Playa 3 showing a less developed smectite morphology (26,000X). Bar equals 1.0pm.
Figure 5.21. X-ray spectra of smectite in Figure 5.20. The chemical formula is Ko.33(Si3 49Alo.5i)(Ali 22Mgo.42Fe()36)Oi„(OH)2nH20.
74
I
• ' . «
Figure 5.22. TEM of several plates of muscovite from Playa 2 stacked upon each other (20,000X). Bar equals 1.0|Lim.
l i-^j -l?3f IG:07;58
V'*rt= 203 c: yrmtmr eset«
Di;;c =
Lifif J Gnm^MifKi i ) IM^NlfitfwRKio
Q]HR
203 sees 19asecs
0.030 -- ^e- 10.230 keV . 10.1i?-
Figure 5.23. X-ray spectra of muscovite in Figure 5.22. The chemical formula is Ko.98(Si3,i5Alo85)(Ali.45Mg().3iFe().25)Oi,)(OH)2nH20.
75
Figure 5.24. TEM of mica from Sevenmile Basin (13,000X). Notice the cracks forming. Bar equals 2.0)im.
Figure 5.25. X-ray spectra of mica in Figure 5.24. The chemical formula is Ko.86(Si3.i8Alo82)(Ali.48Mg{)3iFeo22)Oi,)(OH)2nH20.
76
Figure 5.26. TEM of a cluster of minute illite particles from Playa 2 suggesting mineral instability (10,000X). Bar equals 2.0|im.
..•r.-.?r: 16:15:22
Line
0 in
K m
\
I ^.;-: \,'
OMfc M(>HlndM RKIo
pmm
i33 sees 233 sees
8.8997 M ' ' r-^^^H
8.13W 8.14GB ^ • b .
^^B
^
~|
"• 1
I
0.830 10.233 MV ai 0 8
10.110
Figure 5.27. X-ray spectra of particles in Figure 5.26. The chemical formula is Ko.4o(Si3.32Alo68)(Ali.i7Mgo47Feo.4o)Oio(OH)2-nH20.
77
#. k #
Figure 5.28. TEM of weathered illite from Playa 2 with a morphology similar to smectite (20,000X). Bar equals l.Ojim.
Figure 5.29. X-ray spectra of particle in Figure 5.28. The chemical formula is Ko.44(Si3.43Al()57)(Ali 48Mgo.36Feo i6)Oio(OH): nH20.
78
Figure 5.30. TEM of a Fe-rich beidellite taken from Wink (33,000X). Bar equals 1.0pm.
Figure 5.31. X-ray spectra of smectite in Figure 5.30. The chemical formula is Ko36(Si3 56Alo.44)(Aii 39Mgo36Feo200io(OH)2nH20.
79
Thus, it appears there is a relationship between clay crystallinity and morphology,
and with the amount of potassium in the interlayer. In micas, the more potassium in the
interlayer, the better the mineral structure, grading down in quality with decreasing
potassium content. For smectite, the more potassium, the poorer the structure of the
particle. There appears to be a transition between smectite and illite at an interlayer
potassium range of 0.3 to 0.6. Illite appears to be weathering into smectite. This
conclusion is based upon: (1) the lack of well-developed smectite particles, (2) the
smectite abundance in the finer fractions as opposed to the abundance of mica/illite in the
coarser fraction, and (3) the presence of potassium in all smectite particles analyzed.
Kaolinite is a minor mineral in all playa basins. The morphology of kaolinite
(Figures 5.32 and 5.33) is subhedral to anhedral. Crystallinity appears to be better than
illite or smectite, and comparable to purer forms of mica. Figure 5.34 shows a crack
forming in a kaolinite platelet from Playa 2. This is probably due to weathering. Figure
5.35 confirms the mineral to be kaolinitic.
Kaolinite appears to be detrital in origin, and inherited from the surrounding
upland areas. The upland and playa soils studied by Allen et al. (1972) found kaolinite to
be <10%. Under severe leaching and acidic environments, smectite can break down to
form kaolinite. Authigenic kaolinite is not found in any samples analyzed. Percolating
waters are not sufficientiy acidic to alter other clays to kaolinite. Kaolinite, like illite, is
generally found in the coarser fractions. However, both minerals can be found in finer
fractions (Figure 5.36). Both particles appear similar morphologically, but EDS reveals
kaolinitic and illitic compositions (Figures 5.37 and 5.38).
80
^1 - s
Figure 5.32. TEM of fine well developed pseudo hexagonal plates of kaolinite from Playa 3 (50,000X). Bar equals 0.5pm.
Figure 5.33. X-ray spectra of kaolinite from Playa 3 in Figure5.32, The chemical formula is Al2Si205(OH)4.
8
Figure 5.34. STEM of a "cracked" kaolinite particle from Plava 2
Figure 5.35. X-ray spectra of kaolinite in Figure 5.34. The chemical formula is Al2Si205(OH)4.
82
Figure 5.36. STEM of kaolinite and illite particles from TDCJ.
8
3:-.i.-.f?f 15:41:3: UI, Low f
Line
0 m
Km
269 ::..-:: •"*»:;f;=
GDuntt Cti/NC - IM>llindM Ritio
£33 se:s 233 sees
0.030 10.233 f 10.113 _
Figure 5.37. X-ray spectra of illite particle from Figure 5.36. The chemical formula is K().54(Si3,s6Aln44)(Ali 39Mgi ,Fe Oii)(QH)-nll-0
Figure 5.38. X-ray spectra of kaolinite in Figure 5.36. The chemical formula is Al2Si205(OH)4.
84
s s T " ^
Figure 5.39. TEM of sepiolite/palygorskite from Playa 5 (20,000X). Bar equals 1.0pm.
85
The clay mineralogy appears to be very similar in all playa samples. Only trace
amounts of sepiolite/palygorskite (Figure 5.39) are found. Elemental analysis (Figure
5.19) shows that the smectite forms a compositional series between beidellite and
montmorillonite. The end members for montmorillonite and beidellite are
Eo.33(Ali.67Mgo.33)Si40io(OH)2nH20andEo.33Al2(Si3.67Alo.33)Oio(OH)2-nH20
respectively. Iron-rich beidellite is observed in many soils as discussed by Tessier and
Pedro (1987), Borchadt (1989), and Robert (1972). Wilson (1987) presents data that
show many soil smectites tend to fall in the montmorillonite-beidellite series. Most soil
smectites, however, cluster in the Fe-rich beidellite area of the graph. The Randall
smectites analyzed do not cluster in the Fe-rich beidellite area, but do lie in the
montmorillonite-beidellite series. Table 5.8 lists the chemical formulae used for
elemental analysis. Table 5.9 lists the compositions of the illitic particles analyzed from
all seven basins.
Nontronite (E0.33 Fe2(Si3.67Alo.33)Oio(OH)2nH20) is rarely found in soils, except
as a weathering product of basic rocks (Sherman et al., 1962). Only two smectite
particles analyzed in this report fall in the nontronite (Fe-smectite) field. This may be a
result of iron coating the particle. The probability of these two smectite particles being
nontronite is questionable.
Typically, geologic smectites can form from the alteration of volcanic ash (Grim
and Giiven, 1978). Although volcanic ash is present in many playa basins on the
Southern High Plains, it was not observed in the playa basins studied. The lack of
observable volcanic ash does not preclude it from being a component of the sediments.
86
The ash could have been weathered away. Beidellite can be a weathering product of
rocks with mica and chlorite, because the required tetrahedral charge needed is already
present. Montmorillonite can form pedogenically from a solution high in Si, Al, and Mg
(Borchardt, 1989).
87
Table 5.8. Table of smectite chemical formulae used in elemental analysis in Figure 5.19.
Sample location
Playa 2
Playa 2
Playa 3
Playa 3
Playa 5
Playa 5
Vance
Vance
Sevenmile basin
TDCJ
Wink
Wink
Formula
Ko.26(Si3.77Alo.23)(Ali.32Mgo.4lFeo.27)Oio(OH)2-nH20
Ko.38(Si3.54Alo.46)(Ali.i2Mgo.44Feo.44)Oio(OH)2-nH20
Ko.29(Si3.63Alo.37)(Ali.25Mgo.47Feo.28)Oio(OH)2-nH20
Ko.33(Si3.49Alo.5l)(Ali.22Mgo.42Feo.36)Oio(OH)2-nH20
Ko.3o(Si3.52Alo.48)(Ali.47Mgo.44Feo.08)Oio(OH)2-nH20
Ko.23(Si3.36Alo.64)(Feo.8lAlo.54Mgo.42)Oio(OH)2-nH20
Ko.35(Si3.58Alo.42)(Ali.7oMgo.22Feo.08)Oio(OH)2-nH20
Ko.o7(Si3.82Alo.i8)(Ali.2iMgo.63Feo.i6)0,o(OH)2-nH20
Ko.22(Si3.65Alo.35)(Ali.05Mgo.63Feo.32)0,o(OH)2-nH20
Ko.i8(Si2.57Ali.43)(Mgi.o5Feo.6iAlo.34)Oio(OH)2-nH20
Ko.36(Si3.56Alo.44)(Ali.39Mgo.36Feo.25)Oio(OH)2-nH20
Ko.08(Si3.78Alo.22)(Ali.35Feo.8oMgo.35)Oio(OH)2-nH20
88
Table 5.9. Table of chemical formulae for illitic particles analyzed by EDS. Note the decreasing interlayer potassium content.
Sample location
Playa 2
Sevenmile basin
Playa 3
Sevenmile Basin
TDCJ
Vance
Wink
Playa 5
TDCJ
Playa 3
Vance
TDCJ
Playa 2
Playa 2
Formula
Ko.98(Si3.15Alo.85)(Ali.45Mgo.3lFeo.25)Oio(OH)2-nH20
Ko.9i(Si3.i5Alo.85)(Ali.52Mgo.32Feo.i6)Oio(OH)2-nH20
Ko.87(Si3.23Alo.77)(Ali.53Mgo.36Feo.06)Olo(OH)2-nH20
Ko.86(Si3.18Alo.82)(Ali.48Mgo.3lFeo.22)Olo(OH)2-nH20
Ko.86(Si3.23Alo.77)(Ali.45Mgo.34Feo.2o)Oio(OH)2-nH20
Ko.85(Si3.34Alo.66)(All.5oMgo.36Feo.l4)Oio(OH)2-nH20
Ko.74(S i3.18 Alo.82)( Al l .52Mgo.33Feo. 16)01 o(OH)2- n H 2 0
Ko.74(Si3.09Alo.9l)(Alo.77Mgo.62Feo.62)Oio(OH)2-H20
Ko.7o(Si3.25Alo.75)(All.53Mgo.35Feo.l2)Olo(OH)2-H20
Ko.69(Si3.23Alo.67)(All.42Mgo.3lFeo.2o)Olo(OH)2-H20
Ko.63(Si3.26Alo.74)(All.45Mgo.34Feo.2l)Oio(OH)2-H20
Ko.54(Si3.56Alo.44)(Ali.39Mgo.39Feo.22)Oio(OH)2-H20
Ko.44(Si3.43Alo.57)(All.48Mgo.36Feo.l6)Olo(OH)2-H20
Ko.4o(Si3.-32Alo.68)(Ali.i7Mgo.47Feo.4o)Oio(OH)2-H20
89
Applications of this Research
The mineralogy of the Randall soils in the playa basins studied for this report,
have a high clay content (>55%); specifically smectite and illite. Large amounts of clay
can have several affects upon soil properties. Randall clay minerals have an effect on the
properties of playa basins for the following reasons:
1. The high smectite content can reduce permeability through the basin.
2. Once the smectites clays are wet, swelling and dispersion will occur. This will also reduce the soil permeability (McNeal et al., 1966).
3. The pH of the recharging waters favor smectite dispersion which can clog pore openings further reducing permeability (Suarez et al., 1984).
4. Smectites are very fine (<0.5 |xm). The surface area of these clays is very large which increases CEC.
5. A high CEC will allow clays to retard the movement of metals, organic matter, or any particles with a positive charge.
6. Transformation smectites are forming in playa basins due to the breakdown of mica/illite.
7. No increase in kaolinite content compared to the interplaya area is found. This suggests that waters are not sufficientiy acidic to breakdown smectite into kaolinite.
90
CHAPTER VI
CONCLUSIONS
The bulk Randall soil samples in the playa basins studied have a high smectite and
illite/mica content (>55%) with minor amounts of kaolinite (<10%). No other clay
minerals were observed in significant quantity. All smectite particles analyzed contain
some interlayer potassium. The potassium is a result of illite/mica breaking down to form
"transformation" smectite. The better defined smectite particles contain a low interlayer
potassium content (<0.20) while the better defined mica/illite particles contain a high
interlayer potassium content (>0.80). The intermediate range of interlayer potassium
(0.20-0.80) indicates mixed layered mica/smectite. The poorly developed illite particles
have lost some interlayer potassium, decreasing their crystallinity. As the potassium 1*5
lost, smectite begins to form. With the continued loss of potassium, a more coherent
smectite structure can form. It is unclear what is replacing the potassium in the interlayer.
The smectite tends to fall in series between montmorillonite and beidellite with
trace amounts of nontronite(?). All smectite particles contain some octahedral iron and
magnesium. Calcium was seldom found in any clay particles. The more developed
smectite particles tend to be montmorillonitic. Smectite particles falling in the beidellite
range tend to cluster in the iron rich section. These smectites are termed iron-rich
beidellites.
91
Kaolinite comprises less than 10% in all samples examined. The interplaya
regions also contain <10% kaolinite as observed by Allen et al. (1972). Unlike the
smectite and illite/mica content, kaolinite content is not higher in the basin relative to the
surrounding interplaya region. This lack of increase suggests that recharging waters are
not sufficiently acidic to break down the smectite to form kaolinite. No authigenic clay
minerals are observed in any of the basins examined.
Clays, smectite in particular, have the ability to swell and disperse upon wetting
and thus reduce recharge. Smectite swelling can reduce permeability by reducing the
amount of open area in the pores (McNeal et al., 1966). Dispersion can reduce
permeability by clogging pore throats (Suarez et al., 1984). Swelling and dispersion are
enhanced in waters with higher pH ranges. Rainwater and overland run-off generally
have pH values less than 6. The Randall soil clays should exhibit significant swelling and
dispersion upon wetting and so should reduce the amount of recharge to aquifers
underlying the playa basins. Recharge, however, is occurring through the playa basins
(Osterkamp and Wood, 1987; Wood and Osterkamp, 1987; Nativ, 1988; Stone, 1990;
Scanlon et al., 1994; Wood and Sanford, 1994; Wood et al., 1996). In addition to the clay
content, a significant amount of coarse material (>2|Lim) is present.
Generally, clay content decreases with increasing depth reflecting the age of the
basins. As the basin grows, more overland run-off, carrying clay material, is able to be
collected. Consequentiy, the clay mineralogy is similar to the interplaya region with the
exception that the basin contains more clay.
92
Osterkamp and Wood (1987) and Wood and Osterkamp (1987) present a model
for the formation of playa basin. The model^is requires carbonate dissolution beneath the
playa to cause subsidence. Clay mineralogy cannot confirm the validity of this model.
To dissolve the carbonate, organic matter must be oxidized to form carbonic acid.. Acid
solutions should enhance the formation of authigenic kaolinite. However, data on pH
values of Randall soils show they are only slightiy acidic (Harris et al., 1972). More
strongly acid percolating waters would be needed for the authigenic formation of
kaolinite. No authigenic kaolinite was observed in the samples analyzed.
Bulk mineralogy does confirm the Osterkamp and Wood (1987) model. No
significant carbonate, with the exception of Sevenmile Basin, was observed on the bulk
powder diffractograms. Once reaction with the carbonate occurs, the pH of the soil water
should rise. The reaction of carbonic acid with carbonate may explain the lack of
authigenic kaolinite.
Cation exchange capacity (CEC) of soils was determined by ammonium acetate
saturation and is an indirect measure (as opposed to soil column test) of contaminant
attenuation. The CEC of the Randall soil clay is high (>80 meq/lOOg of clay). The fine
smectite (<lpm) observed under the electron microscope has a large surface area. Values
of CEC are larger for finer smectites due to the increased surface area available for
exchange. The clays present in playa basins do have the ability to retard the movement of
any positively charge contaminant. More detailed studies of the Randall clays must be
performed to quantitatively determine the attenuation of contaminants through playa
basins.
93
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