QUATERNARY RESEARCH
13, 172 -186 (1980)
Holocene Desert Soil Formation under Sodium Salt Influence in a
Playa-Margin Environment
FREDERICK F. PETERSON
Plant, Soil. Water Science Dil'isiotl. Unil'ersity
(~r
Ne\'ada. Renu. Reno. Nevada 89557
Received March 20. 1979
A visually prominent desert soil with a horizon of clay accumulation (Typic Natrargid) has
formed under an arid climate in Panamint Valley, California, in sandy, very calcareous, saline fan
alluvium in less than about 3500 yr, and probably less than 2000 yr. Such soils can be used as
stratigraphic markers, but could be confused with other desert soils with clay-accumulation horizons (Haplargids) which occur much more commonly on desert alluvial fans, are mostly late
Pleistocene or older, and do not form in parent materials that are still calcareous. This Natrargid
formed in a playa-margin environment, where clay for translocation and sodium salts that engender
rapid clay movement probably were provided by dust fall.
INTRODUCTION
Soil horizons can serve as stratigraphic
markers for geomorphic and archeological
studies of Quaternary deposits. Some soils
also can be age indicators, but for either use
the pedogenic status of the soil horizons,
their kind and degree of alteration, and the
conditions of formation should be explicitly
identified to prevent misinterpretations.
Layers merely identified as "weakly" or
"strongly developed soil horizons" may be
such for reason of soil structure, consistence, the relative color, clay, calcium carbonate, or opal content, or combinations of
these properties. Too frequently, no evidence is given for pedogenic alteration, as
compared with geologic origin, and the
rather different times and conditions of
formation for different pedogenic alterations are not considered.
Clay, carbonate, or opal accumulation-to form argillic, calcic or
petrocalcic horizons, or duripans-are the
most prominent evidences of soil formation
in arid regions, and we now have considerable understanding of rates and conditions
for their pedogenic accumulation. This
paper describes relatively rapid, pedogenic
clay accumulation in the natric horizon of a
Natrargid formed in highly calcareous alluvium, apparently under conditions of
172
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Copyright © 1980 by the University of Washington.
All rights of reproduct.ion in any form reserved.
marked soil salinity and aridity. 1 Natrargids 2 are a subclass of Aridisols, or
pedogenic desert soils, having a B horizon
of both iHuvial clay and exchangeable
sodium accumulation called a natric horizon (USDA, 1975, p, 28, 163). The more
common Haplargids-which have an analogous ilIuvial clay B horizon, or argillic
horizon, but lack significant exchangeable
sodium accumulation in it-most commonly occur on late Pleistocene or older
surfaces and do not seem to form in even
moderately calcareous parent material until
the carbonate has been leached. These two
similar desert soils can be confused. Both
can serve as stratigraphic markers, but their
implied ages and formation conditions are
quite different.
In arid, southern New Mexico, a few
Haplargids with minimal argillic horizons
have formed in as little as 1100-2100 yr in
high-gravel (i.e., >50% by volume), lowcarbonate (i.e., <2% CaC0 3 equivalent)
J This work was part of an unpublished. cooperative
archaeological study directed by E. L. Davis. Great
Basin Foundation, San Diego. Calif. It was done while
the author was a member of the Soils and Plant Nutrition Department, University of California, Riverside.
2 In the literature prior to about 1970, Natrargids
were included among soils called "Solonetz" or
"Solodized-Solonetz" soils.
173
HOLOCENE PLAYA-MARGIN SOILS
parent materials. The youngest Haplargids buffer (Grossman and Millet, 1961). The
in low-gravel, low-carbonate parent mate- percentage water-soluble salts and CaC03
rials are some 2200-4600 yr old. These equivalents were calculated from weight
parent materials either contained some clay losses after dialysis. Soluble salt concenfor translocation, or the soils received clay tration in a saturated paste extract was
as dust fall. Soils with argillic horizons do measured by conductivity, and the sodium
not occur in high-carbonate (i.e., > 15% adsorption ratio (SAR) was determined from
CaC0 3 equivalent) parent materials of soluble-cation concentrations (Richards,
Holocene age (Gile, 1975, pp. 356-357). 1954). Cation exchange capacity was meaHowever, most desert soils with argillic sured by the method of Okazaki et al. (1962).
horizons formed in either high- or low- Organic matter was determined by wet oxicarbonate parent materials in this area are dation (Richards, 1954). Soil pedon descripoflate Pleistocene age, or older, and appar- tions and identifications follow soil survey
ently formed primarily under more effective terminology (USDA, 1975).
leaching conditions of pluvial intervals
STUDY SITE DESCRIPTION
cooler and moister than the Holocene (Gile
The Natrargids described here occur on
and Hawley, 1968, p. 715). In arid western
an alluvial-fan skirt at Lake Hill, a small
Nevada, where argillic horizons formed in
dolomite hill in northern Panamint Valley,
arkosic sands, chemical weathering and
California (Fig. 1). This valley is a long
clay movement have been too slow to form
structural basin bounded on the east by the
argillic horizons in less than 12,000 yr, or
Panamint Range and on the west by the
since the late Pleistocene (Nettleton et al.,
Argus Range. Playas separated by a low
1975). In such areas, desert soils with argilalluvial divide now occur at the vaHey's
lic horizons and low gravel contents can be
thought of as late Pleistocene or older relicts.
Natric horizons can form relatively much
more rapidly in low-gravel, high-carbonate,
clay-containing parent materials under the
dispersive influence of sodium. Many occur
on sediments no older than late Pleistocene,
or in playas, or on the margins of present or
c_
wI'
Pleistocene lakes in situations suggesting -,-T
,.L
Holocene age (USDA, 1975, pp. 19, 28,
/
163). Alexander and Nettleton (1977) reported Natrargid formation in less than
en
'P'
6600 yr in loamy, calcareous 0- 3% CaC0 3
~
equivalent), saline (conductivity of satura~
-\
tion extract = 4-30 mmhos/cm), floodplain
-1J
sediments in arid western Nevada. This
I'
V
V
("
paper describes an even more rapid Natrar"'N
"
v
gid formation in a yet more calcareous,
'"
'"
I v-t7"'
more saline material.
-<.l
--
(;)
,/
('0
METHODS
Particle-size analyses were made by pipet
method for fine earth from which (a) soluble
salts were removed by protracted dialysis
against water, and (b) carbonates were removed by protracted dialysis against pH 5
~
0
0
0_5
'1-"
km
FIG. I. Location of the Lake Hill, Panamint Valley,
California site, the bulldozer-cut exposures, and the
major landforms.
174
FREDERICK F. PETERSON
north and south ends, but roughly 100km-Iong and 280-m-deep Pleistocene lakes
fed by local drainage and spillover from the
Pleistocene Searles - China - Owens Lakes
system periodically filled the Panamint
basin until it, in turn, spilled over into
Death Valley as late as Tahoe time, and
perhaps as late as early Tioga time. During
latest Tioga time, a lake about 60 m deep
filled the southern playa and a separate,
very shaHow lake (about 6 m deep) filled the
northern playa (Blackwelder, 1954:
R. S. U. Smith, 1975, 1978). Lake Hill
stands between the eastern shore of the
I3-km-Iong northern playa and the toeslope
ofthe 2- to 4-km-wide al1uvial-fan piedmont
of the Panamint Range. The playa (472-m
elevation) is 0.6-1.3 km wide west of Lake
Hill, and extends 9 km to the south: both
are directions from which storm winds
carry eolian sediments. The Argus Range
alluvial-fan piedmont, to the west, is some 6
km wide.
The Panamint Valley floor is arid, hot in
summer, and cold enough for transitory
snowfall in winter. Mean annual precipitation is only 10 em, but much comes from
regional winter storms that have been seen
to moisten effectively a shallow soil layer.
Mean-maximum July temperature is 41°C,
and mean-minimum January temperature is
OQC (Elford, 1970). Except for sparse
shrubs, e.g., creosote bush (Larrea tridentata), the study site is barren.
The site proper comprises (1) the 145-mhigh, 3-km-Iong hill, (2) its surrounding 45to 140-m-wide, very gently sloping,
anuvial-fan skirt grading to the playa, or to
the Panamint-Range-fan piedmont, and (3)
the playa. Lake Hill is a barren, rocky,
sloping to steep-sided fault block of highly
shattered and partially recemented, dense,
grey dolomite. It has only a very shallow,
rocky soil mantle.
The playa is actively filling with verypale-brown (lOYR 7/3, dry; 10YR 5/4,
moist), sticky, plastic, gravel-free, loamy
sediments from the Panamint and Argus
Ranges. The surficial playa sediment contains about 2% water-soluble salts. 20%
calcium and magnesium carbonates, M1
sand (mostly fine and very fine sand), 7S7r
silt, and 19o/r clay near the site. Roughly
equal proportions of carbonate occur in the
sand-, silt-, and clay-size fractions. Weathering and erosion of the Lake Hill dolomite
mass itself must contribute only miniscule
sediment to the playa, and its alluvial-fan
skirt has been graded to a playa base level
largely controlled by erosional events on
the great fan piedmonts and mountain
fronts.
The Lake Hill fan-skirt sediments contain
much dolomite sand and fine gravel from
the hill's bedrock, but several relations
suggest the finer material in the fan-skirt
soil was blown from the playa and deposited directly on the fan skirt, or deposited
on the hill and then washed back onto the
fan skirt. First, eolian sand is now collecting as thin, discontinuous mantles at the
base of the steep hillslopes and washing
back onto the fan skirt through rills and
distributary channels (Fig. 2). Second, the
surficial playa sediment and fine earth
component of the fan and hill soils have
similar compositions and brownish colors
when compared with the gray dolomite.
The playa sediment and soils all have clay
fractions in which montmorillonite is dominant, mica and kaolinite contents are moderate, and both calcite and dolomite are
present. Their fine earth fractions are
20-40% carbonates, whereas the dolomite
is about 95% carbonates. Third, the A and
B horizons of the very shallow soil on
gently sloping ridge crests just above the
fan skirt apparently formed in eolian material. Since this soil is approximately contemporaneous with those of the hill slopes
and fan skirt, or only slightly older, it is
evidence that eolian material probably was
deposited on the hill, from which it was
available to be washed back onto the fan
skirt. The ridge-crest soil has largely
gravel-free A and B horizons with only
20- 26% carbonates in the fine earth. The
underlying Cca horizon is considerably
thinner than the combined A and B horizons, is extremely gravelly and stony, and
HOLOCENE PLAYA-MARGIN SOILS
175
FIG. 2. A low scarp between the modern Rainbow fan surface. in the foreground, and remnants of
the late-Holocene Lake Hill fan surface. The spade is stuck in an outcrop of the natric horizon formed
on the Lake Hill surface. A thin mantle of eolian sand lies at the base of the rocky slopes of the
dolomite hill. The Panamint Range is in the far background .
.
'
grades to shattered dolomite bedrock which
contains only 5% acid-insoluble residue. If
the approximately 75% noncarbonate material of the A and B horizons is residue from
weathering of the dolomite under an arid
climate, much larger volumes of pedogenic
carbonates would be expected to have accumulated in the Cca horizon than occur.
Both the low gravel content of the A and B
horizons, and the small volume of
pedogenic carbonate, suggest eolian deposition.
ALLUVIAL-FAN SKIRT
The datable Natrargid occurs on the 15to 33-m-wide, alluvial-fan skirt on the west
side of Lake Hill. Maximum fan slopes are
about 7% at the top, but most are from 4 to
less than 2%. The fan abuts the steep hill
slopes abruptly and its gravel-paved al-
luvium has a distinct terminus on the playa.
The fan skirt comprises two differently
aged surfaces. The older, relatively stable
Lake Hill fan surface is marked by the
prominent, though thin, grey Av horizon 3
and reddish-brown B2t horizon of a Natrargid, and is being shallowly dissected in
many places (Fig. 2). The resultant,
younger, inset, Rainbow fan surface heads
at the hill sideslopes, is cut from a few to
about 30 cm deep into the older surface,
and grades onto the playa beyond remnants
of the older surface. The younger surface
has a thin, grey Av horizon, but either only
:l The" Av" horizon notation is an informal one denoting vesicular porosity; it is not found in official soil
survey pedon descriptions. There these massive.
crusting. vesicularly porous. surficial horizons are
noted as Al horizons.
176
FREDERICK 1'. PETERSON
an incipient, slightly reddened B2 horizon,
or no B2 horizon. It has common distributary rills across it and is an active surface of
sediment transport. Eroding outcrops of the
reddish-brown nat ric horizon at the scarped
margins of the older Lake Hill surface remnants suggest the younger surface is being
expanded laterally. In some places, fresh
distributary rills still cross Lake Hill surface remnants, but most hillslope drainage
bypasses the older surface and flows across
the younger. Both fan surfaces have a
sparse desert pavement of 1- to 3-cm dolomite pebbles and coarse sand; pebbles are
somewhat more closely spaced on the older
surface. Artifacts (i.e., exotic obsidian
chips) are found on both surfaces and in the
fan alluvium under at least the older surface.
The Rainbow surface is a modern surface
contemporaneous with the playa, to which
it grades, and with active portions of the
Panamint and Argus fan piedmonts which
also grade to and feed sediment to the
playa. The Lake Hill surface toeslope
merges topographically with the Rainbow
surface. The distinctive, reddish-brown
natri c horizon of the Lake Hill surface ends
where the two surfaces apparently merge:
no exposures were seen where Rainbow
sediments overlie and bury the Lake Hill
surface soil horizons.
ALLUVIAL-FAN SKIRT AND PLAYA
SEDIMENT STRATIGRAPHY
Sediments underlying the alluvial-fan
skirt and playa margin were exposed in
three bulldozer cuts, originally numbered 1.
2, and 6. Stratigraphy was established in cut
6, and confirmed in the other two cuts
(Figs. 1, 3, and 4). The sediments separate
into two units of major significance: an
upper unit of merging alluvial-fan skirt (AF)
and playa (AP) sediments (AFAP, where
imbricated), and a lower unit of basal fan
gravel (BF) and basal lacustrine (BL) sediment.
Pleistocene Basal Sediments
From about station 12 (meters, horizontal
distance) on out past station 29, in cut 6
(Fig. 3a), the major unconformity between
the units is underlain and marked by a distinctively grayish, very friable loam or
gravelly loam Alb horizon (i.e., a buried
horizon of humus accumulation), which has
4% oxidizable humus, as compared with the
humus-free overlying sediment. The Alb
horizon is underlain by a carbonate-rich,
light-gray (N 7/, dry; N 5/, moist) silt loam
horizon beyond station 19. This peculiar
horizon is shot through with l-mmdiameter, vertical, yellowish-brown-claycoated root channels. Because it has the
prominent clay skins characteristic of many
argillic horizons, it is noted as a B2tb horizon in Fig. 3. Between stations 12 and 19,
the Alb horizon is underlain by a white, friable, highly carbonate-impregnated,
gravelly loam Ccab horizon, which looks
like marl and is so different in site and
character from the Cca horizons of the hill
soils that it is informally called the "marly"
horizon (M) here. This horizon also is shot
through with vertical 2- to 3-mm-diameter
root channels, but these are surrounded by
a hard, white, carbonate encrustation.
Below these adjacent B2tb and "marly"
horizons is a 5- to 8-cm-thick, black,
peaty-feeling Ob horizon (i.e., buried organic soil horizon) which contains some 7%
oxidizable humus. and considering its consistence. probably a much larger amount of
nonoxidizable, carbonized, peaty organic
material. A sample taken at station 16
was dated at 10,020 ± 120 HC yr B.P.
(UCLA-989). Between stations 14 and 15,
the Ob horizon divides into numerous, thin,
gray layers that merge into the "marly"
horizon. and suggest alternating deposition
of humus-rich sediment and marl. Several
thin. dark-gray layers of apparent humus
accumulation occur between the Alb and
Ob horizons, indicating that the sediment
which buried the Ob horizon accumulated
slowly enough to allow periodic humus accumulation. In cut 2 (Fig. 4), carbonized
reeds taken from the upper part of a correlative Alb horizon dated at 10,520 ± 140
HC yr B.P. (UCLA-990). A correlative Alb
also occurs in cut I (Fig. 3b). The Alb and
eA)
-
Cut 6. north wall
upper
playa margin, 35m
.. --- Lake Hill ton surface ---- ..
,Av.:...~
..."-
"'':_'''"'_'''''':.'''.-'''''"'''''''''"'''''''''''''''fl"",·,""""m:''(;-;A:-:F~);-::"~",~""~",:::;"";;;;~,;;;;",,,,,,"""";;;"";r,;",m",,;;;l;.,,,;m,,,ii 'lIi iul,i i'Iijjljlliilllliililiiilliiilllil1d,iiilliillliiiIITiniiil!Iiii!!'iiiTu 82t 1IIIIIIillll" ' _'-";
------- -- --------------------3"
83
.~ .....~-:i!e'"
Gm~......
30
..
-3 Q;
E
...... ~'.r.'.I.!! U.'\ll tIt r~)·'-..J\>l(BF)
"~I:
2'5
~~~-c.~..
··)"i.,,-M....,...~r--­
(AP)
~k"1'l"M~«.~/~#~Alb
:/Ii
? .... _ _:.t.:
• !it----- 82 tb
II)
::r::
or
o("j
m
z
-4
\ dated Ob horizon 10.020 ± 120 14C yr B.P (UCLA 9S9)
2'0
'0
1'5
5
6
m
."
r
~ ~
hillslope-0 -.. If'~I"v.;
~Av
.......... .'~J~. "'"'82f
2-
4-
.
6-
o
.... ··Ceo
dolomite
bedrock
>
-<
)-
(B) Cut I, south wall
Hill fan surface --- - - ....... -mergence lone - --
--~"--Roinbow
i:)-
fan surface--- ....
~
Z
playa margin. 9m -
playa surface level-
.
10
;..
.
20
.
meters
30
'"o
r:::
'"
(AP) ...
~p~fj);pp}1'~#~
40
50
FIG. 3. Stratigraphic diagrams for bulldozer cuts 6 and 1 on the Lake Hill alluvial-fan skirt. Members of the basal Pleistocene unit are: (BL) basal
lacustrine sediments, and (BF) basal fan gravel. Members of the overlying Holocene unit are: (AP) playa sediment, (AF) alluvial-fan-skirt alluvium, (AFG)
very gravelly f;m alluvium, and (AFAP) imbricated fan and playa sediment. Soil horizon notation is explained in the text; soil lithological discontinuity
notations are not used. Vertical exaggeration is 1.5 x .
....
-.I
-.I
178
FREDERICK F. PETERSON
Cut 2. east wall
~ __ Rainbow fan surface----: ·Lake Hili fan surface
-2
IO,520! 140 14C yr BP
subhorizons
,
,
15
10
4
(UCLA 990)
5
0
meters
FIG. 4. Stratigraphic diagram for bulldozer cut 2 in
the Lake Hill alluvial-fan skirt. See Fig. 3 for key to
symbols. Vertical exaggeration is 1.5 x .
Ob horizons, or zone of humus accumulation, date the basal lacustrine sediments as
late Pleistocene.
Since "marly"-horizon sediments overlap the basal fan gravel (BF), it is as old or
older. Although only some of the dolomite
pebbles and cobbles in the basal fan gravel
are rounded, and the gravel is not stratified,
it does occur in a position that suggests it
could be a poorly worked beach deposit. Its
large pebbles and cobbles (8-13 cm diameter), compared with the fine gravel of the
later alluvial-fan skirt, might also reflect
strong erosional stripping of Lake Hill in
late Pleistocene time. Carbonate coatings
are common on the bottoms of pebbles and
suggest that the basal fan gravel contains a
relict Ccab horizon, but there is no evidence of an overlying, relict B horizon.
The Ob horizon (Fig. 3a) is so peaty it
would be expected to have formed in a
continuously wet regime, i.e., a shallow
lake margin or marsh. Pollen from this horizon " ... showed sedges and cattails
(Typha tatifolia or hybrids of T. lat(folia)
were locally abundant" (Mehringer, 1967,
p. 187). The overlying Alb horizon probably
formed in a moist. but occasionally dry regime, for it has a lower humus content and
nonpeaty consistence. The underlying, discontinuous, or pod-like "marly" horizon
exposed in cuts I and 6 may have formed at
the edge of a marshy area by biological car-
bonate precipitation, or. as suggested by
the carbonate root-casts. by plant transpiration and resultant carbonate precipitation
from bicarbonate-charged water. The root
casts suggest that the marl deposition and
humus accumulation in the Alb horizon occurred contemporaneously.
The neutral grey matrix color of the 82tb
horizon underlying the Alb and Ob horizons
also suggests a strongly reducing environment of a marsh or shallow lake bottom.
However, the yellowish and reddish-brown
color of the c1ayskins that line the open,
vertical root channels and some cracks
between blocky structural units do not indicate reducing conditions. In cut 6, these
clay-lined root channels and cracks extend
from below the Ob horizon up through it to
the base of the Alb horizon, and indicate
that clay deposition occurred after the Ob
horizon was buried, and that the Alb horizon formed under less-wet, perhaps periodically dry conditions. The clayskins
probably were formed by pedogenic clay
iIluviation because they originate at the
base of the Alb horizon, but they might
have been deposited by infiltration of
muddy water during the first stages of burial of the Alb horizon by Holocene playa
sediment.
Holocene Sediments
The Lake Hill alluvial-fan skirt is formed
of finely stratified coarse sand and fine
gravelly sandy loam (AFG) in its upper
parts, but rapidly grades to finely stratified
medium sand, loamy fine sand, and fine
sandy loam with common, thin, discontinuous strata of coarse sand and fine dolomite
gravel toward its toeslope (AF). At about
station 16 (Fig. 3a) the fan alluvium
abruptly thins and is underlain by stratified,
gravel-free. coarse sand-free, pale-brown,
and light-grey playa deposits of well-sorted
medium sand, loamy fine sand, very fine
sandy loam, and coarse silt textures (AP).
All fan and playa sediments are calcareous
and saline.
Several 2- to 50-em-thick and meter-wide
lenses of gypsum and salt-cemented fine
HOLOCENE PLAYA-MARGIN SOILS
gravel (Gm) occur both in otherwise uncemented gravel (AFG) and as isolated,
cemented gravel lenses in the middle
reaches of the fan at 60- to 9O-cm depth.
Similar cemented lenses were found at
about the same contour in pits along the fan
skirt, including the soil-sampling site (Table
1). They are not regularly related to the
overlying natrie horizon, and are interpreted as erratic concentrations of salts in
these very saline sediments, rather than as
a pedogenic horizon.
Playa and Fan Sediment Ages
The playa sediments overlying the Alb
and Ob horizons are less than about 10,000
yr old. Because the alluvium forming the
179
Lake Hill and Rainbow fan surfaces overlaps or grades to the playa sediment, it is no
older, and probably younger, than the
upper playa deposits (Fig. 3). A closer dating for the Holocene playa deposits may be
inferred by correlation with stratigraphically very similar deposits in the China
Lake and Searles Lake basins, just southwest of the Panamint basin. Those adjacent
basins were occupied by shallow Holocene
lakes related to a pluvial event beginning
about 4000-6000 yr ago, and ending about
2000-3000 yr ago (Smith and Davis, 1978,
pp. 167, 172). At Searles Lake, the uppermost lacustrine deposit is identified by
Smith (1968) as the "Overburden Mud"
unit, or alternatively as unit "D" (G. I.
TABLE 1
PEDON DESCRIPTION FOR THE NATRARGID ON THE LAKE Hill Sl:RFACE COMPONEl"T OF THE
ALLUVIAL FAl" SKIRT"
Horizon/
Depth (cm)
Description
Pavement
1-0
Dolomite pebbles. \- 3 cm diameter. solution pitted and unpitted. not varnished, cover 5·-10% of surface; quartz and dolomite very coarse sand covering 15~90% of surface.
Av
0-0.6
Light-gray (lOYR 6/1) sandy loam, grayish-brown (lOYR 5/2) moist; massive,
cracked into 6 to to-cm polygons; hard, friable. slightly sticky, nonplastic;
violently effervescent; abrupt smooth boundary to:
B2t
0.6-20
Light-reddish-brown (5YR 6/4) sandy clay loam grading to loam with depth,
reddish-brown (5YR 4/4) moist; weak medium to coarse prismatic grading to
massive with depth; slightly hard, very friable, sticky. plastic; violently effervescent; a few fine gypsum crystals: clear wavy boundary to:
B3
20-41
Banded, or lamellar light-reddish-brown (5YR 5/6) fine sandy loam and lightgray (lOYR 7/1) fine sand, reddish-brown and gray (5YR 4/4 and IOYR 6/1)
moist; massive; slightly hard to loose. very friable to loose, nonsticky. nonplastic: about ¥.J of horizon consists of the 1- to 2-cm-wide, light-reddishbrown bands of clay-coated sand which are more widely spaced with depth;
violently effervescent; abrupt smooth boundary to:
Cl
41-51
Light-gray (10YR 61l} fine sandy loam to silt loam. grayish-brown (lOYR 512)
moist; massive; hard, firm, non sticky , nonplastic: violently effervescent;
slakes in water; many fine gypsum crystals: similar 10 "Gm"-cemented lenses
occurring in cui 6; abrupt smooth boundary to:
C2m
51-53
Light-gray (I0YR 6/1) sandy loam, dark gray (lOYR 4/1) moist; massive;
strongly cemented by salts; violently effervescent: like the "Gm"-cemented
lenses occurring in cut 6,
" Distributary rills were braided across the soil surface at this sampling site some 15 m downslope from the
upper fan margin and 8 m north of cut 6 (Fig. 3A),
/i Lithological discontinuities (USDA, 1975, p. 462) involving contrasting textures or mineralogies inherited
from parent material strata are not noted since they are potentially numerous in this stratified alluvium, and since
all horizons but the C horizon are postulated to have been sand or loamy sand textured initially. The relatively
silty C horizon probably was formed from sediments quite contrasting to the overlying sandy fan alluvium.
180
FREDERICK F. PETERSON
Smith, 1978); it appears to correlate with
the playa deposit (AP) at Lake Hill,
Panamint Valley. Deposition of Searles
Lake unit "D" was followed by a period
of soil formation (Smith, 1968, p. 304); the
Natrargid on the Lake Hill alluvial-fan skirt
would be correlative with that soil. The deposition of the Searles Lake unit "D" was
preceded by a period of complete lake recession and soil formation (" soil CD,"
Smith and Davis, 1978, p. 168; G. I. Smith,
1978, p. 4); the Alb- B2tb soil that formed
in basal lacustrine sediment (BL) at the
Lake Hill site is correlative. The period of
"CD" soil formation at Searles Lake was
preceded by deposition of the "Parting
Mud," or unit "C," which is older than
about 10,000 yr (G. I. Smith, 1968, 1978);
the basal lacustrine sediment below the Ob
horizon is older than 10,000 yr and correlative with unit "C." The correlation of the
Lake Hill site playa sediment (AP) with the
Searles Lake unit "D" is considered reasonable by G. I. Smith (personal communication, 1978), but he emphasized that the
only firm date for unit "D" is from a piece
of wood found near the middle of this unit
which had an age of 3520 ± 120 HC yr B.P.
(Stuiver, 1964).
Since the Lake Hill fan-skirt alluvium
(AF), and in particular that forming the
.. Lake Hill surface," is no older, and probably younger, than the playa sediments
(AP), then the fan surface can be considered at least younger than 3500 yr and
probably younger than 2000 yr. The soil
formed on the Lake Hill fan surface is,
therefore, probably younger than 2000 yr.
THE LATE HOLOCENE SOIL
The soil 4 on the Lake Hill fan surface will
be shown to be pedogenic, hence indicative
of geomorphic stability and, thus, stratigraphically significant. It is a fine-loamy,
, In the most general sense, soil is merely earthy
material which contains living material and is potentially capable of supporting plants (USDA, 1975, p. I):
thus soil can be fresh geologic alluvium essentially unaltered by genetic soil-forming processes, or a
pedogenic body.
mixed, thermic Typic Natrargid;' (USDA,
1975, pp. 163 164). Pedogenic soils may be
defined as those containing one or more
altered layers, or horizons, which parallel a
present land surface (or buried or exhumed
surface) and which are somewhere discordant with the geologic structure or fabric of
their parent materials. Altered means an
addition to, or loss from, or mechanical
rearrangement of what reasonably can be
assumed to have been the parent material
(i.e., "geologic" material as contrasted
with resultant "pedogenic" soil). The alteration, such as humus, or clay, or carbonate
accumulation or loss, or soil structure formation, characterizes the layer and ditIerentiates it from underlying or overlying
layers. Parallelism to a land surface is evidence that the alteration is somehow related to processes dependent on infiltration
of meteoric water from the land surface to
generally uniform depths, but in variable
amounts and frequencies for different depth
zones with different etIects. Thus, ilIuvial
clay must accumulate below a source or
transmittal horizon-the eluvial A
horizon-and pedogenic CaCO;! will accumulate at yet greater depth at the limit of
common moisture penetration in arid climates. Discordance with parent material
structure or fabric demonstrates that the
alteration postdates emplacement or formation of the parent material. Discordance
can be megascopic, as where an entire argillic horizon passes with angular discordance through weathered, dipping, geologic
strata which have been truncated by an erosion surface, or as where a petrocalcic horizon passes from well-sorted alluvium into
contiguous, hillslope, colluvial deposits.
Or, the discordance may be a nearly microscopic relation to fabric, as where illuvial
clay in an argillic horizon bridges and cements alluvial sand grains and pebbles in a
fashion never seen in the freshly deposited
:, The properties of most. but not all the pedons (or
sampling volumes) satisfy the taxonomic criteria: this
is the usual situation when soils are mapped and identified according to the U.S. Soil Taxonomy (USDA.
1975).
HOLOCENE PLAYA-MARGIN SOILS
material, or as in a prismatic cambic horizon where the horizontal, fine stratifications of a sediment have been disrupted and
mixed, and vertical cracks now appear.
The Av horizon and B2t horizon, or natric
horizon, of the Natrargid are both pedogenic, but only the latter is taxonomically
diagnostic and geomorphically or stratigraphically significant. The soil does not
have a significant pedogenic carbonate horizon; the salt - gypsum impregnated or cemented Cl and C2 horizons encountered in
the sample pedon (Table 1; cf., "Gm"
lenses, Fig. 3a) are discontinuous and, as
stated above, are not considered pedogenic
horizons.
The Av and B2t horizons are 15 and 30
cm thick, respectively, on the uppermost
fan segment (Fig. 3a, stations 0-2), where
the alluvium from which the pedogenic
horizons formed was coarsest (a loamy
medium to coarse sand), but they rapidly
thin downslope and are only about 5 and 18
cm thick at stations 9 to 16, where the alluvium was medium sand, and are a mere 1
and 7 cm thick at station 23, where the alluvium was a fine sand or fine sandy loam.
Beyond station 29, where the Lake Hill fan
surface terminates, and the younger Rainbow fan surface replaces it, there is a 1em-thick Av horizon, but only the slightest
reddening suggests formation of an incipient cambic B. The thinning solum may be
explained by the increasing waterholding
capacity of the progressively finer-textured
fan sediments downslope, hence shallower
precipitation infiltration. Additionally,
sheetflood irrigation from the hills lopes
should be lesser and more widely or erratically distributed downslope, and effective
wetting could have been less. Where sampled (Table 1), the Av horizon is only 0.5-1
cm thick; rills cross the surface here and
may have slightly eroded the soil. However, except for thickness, the horizon is
characteristic for the soil.
The thin Av horizon is light-colored, has
very low humus content, and is massive except for a coarsely polygonal pattern of des-
181
iccation cracks. When dry it forms a
slightly hard or hard crust, with prominent
1- to 2-mm-diameter vesicular pores. Massiveness, polygonal cracking, crusting, and
vesicular porosity are features diagnostic of
surficial loamy soil materials that slake
readily and have been repeatedly saturated
and dried. Size and number of vesicular pores increase with recurrent
saturation-desiccation cycles if the material is not crushed by wheel or animal traffic
(cf., Miller, 1971). Such Av horizons form
in materials as coarse as loamy sand and as
fine as clay loam, but are most common in
sandy loams or silt loams with low clay and
humus contents. They can form in only a
few months. An A v horizon is the first horizon to form in sand-within a few hundred
years, or less-where dust falls on the sand
and is infiltrated; since dust fall seems
ubiquitous in deserts, this is a significant
soil-forming process (Gile, 1975; Peterson,
1977; Yaalon and Ganor, 1973). The 1em-thick Av horizon in the modern, sandy,
Rainbow surface soil is evidence of rapid
formation.
The A v horizon has only a sparse desert
pavement of unvarnished pebbles, but a
thin, very coarse sand mulch covers
15-90% of the surface and obscures the
polygonal crack pattern. Desert pavements
are prominent on arid-region soils that
contain gravel and occur where dust or
loess fall has been slow, or minimal. However, the Av horizon which regularly occurs under the desert pavements, or without a pavement, is an ubiquitous characteristic of desert soils.
The clay increase from A to B horizon
(Table 2 and illuvial clay deposits described
later) qualify the B as an argillic horizon
and its very high SAR value and prismatic
structure qualify it as a natric horizon
(Table 2). Much of the clay-size fraction is
carbonate, and both carbonate and silicate
clay contents increase from A to B horizon;
cation exchange capacities confirm the
acid-insoluble clay distribution (Table 3).
This soil is extremely saline and sodic.
182
FREDERICK F. PETERSON
TABLE 2
PARr/elf-SIZE DISTRIBUTION OF [HE WHOLE SOIL A~[) IHE SOLUBLE. S.-\U-FREE A"ID C\RBON.UE-FREF
FINE EARTH FOR THE LAKE HILL SURFACE NATRARGlD
Fine earth (<;;. of soluble-salt-free fine earth)
Horizon
Av
B2t
B2t
B3
B3
CI
Depth
(em)
0-0.6
0.6-13
13-20
20-30
30-41
41-51
Whole soil
v.eo.s.
1-2 mm
(%)
>5 mm 5-2 mm <2 mm
5
4
6
4
3
3
1
3
<1
3
<1
10
89
86
93
96
94
99
co.s.
1-0.5 mm
m.s.
0.5-0.25 mm
f. ,.
0.25~O.1
mm
S"
C"
S
C
S
C
S
C
16
11
6
2
2
10
5
3
6
9
4
5
5
3
4
3
9
6
8
8
16
6
5
4
6
9
16
14
II
19
34
6
14
10
12
1
0
11
8
11
18
4
Fine earth (% of soluble-salt-free fine earth)
v.f.s.
Horizon
Av
B2t
B2t
B3
B3
Cl
Depth
(em)
0-0.6
0.6-13
13-20
20-30
30-41
41-51
0.1-0.05 mm
Total Sand
2-0.05 mm
Silt
0.05-0.002 mm
Clay
<0.002 mm
._------
S
C
S
C
S
C
S
C
19
16
12
25
28
26
18
14
II
18
18
16
66
56
41
64
92
35
53
40
30
38
49
22
20
16
25
19
2
53
17
14
12
17
8
26
14
28
34
17
6
12
10
20
CaCO"
equiv.
23
13
4
8
20
26
35
32
39
44
" The S columns are for the soluble-salt-free, <2-mm fine earth after dialysis against water.
" The C columns for the soluble-salt- and carbonate-free fine earth after dialysis against pH 5 buffer.
Sodium is the dominant water-soluble cation, followed by Ca, Mg, and even a significant K accumulation. The soluble anions
are dominantly chloride with some carbonate-bicarbonate accumulation in lower
horizons. Soluble sulfate approximates a
saturated gypsum solution (27 me/liter);
undoubtedly larger amounts of gypsum are
present than dissolved (Table 3).
The highly calcareous nature of all horizons and particle-size classes, except possibly the silt fraction in the lower B3 horizon, is indicated by the decreasing percentage of each fraction after protracted dialysis
against pH 5 buffer (Table 2). The increased
silt content of the acid-treated lower B3
horizon material may have been due to accumulation of silty acid-insoluble residue
from decomposed dolomite sand. The particularly high proportions of carbonate silt
and clay in the lower B2t and C 1 horizons
suggest some carbonate precipitation there.
Total fine-earth CaCO;j equivalents range
from 20 to 30% in the solum, levels which
seem to preclude clay iIluviation in soils
lacking dispersive exchangeable sodium.
Contiguous Soils
Bulldozer cut number I extended up onto
a bedrock spur of Lake Hill (Fig. 3b) and
showed that the A v and B2t horizons of the
fan-skirt Natrargid continue onto the hillslopes in what are inferred to be eolian fines
trapped between bedrock outcrops. A
pedon sampled on top of a gently sloping
ridge crest has a I-em-thick Av horizon, a
HOLOCENE PLAYA-MARGIN SOILS
183
7-cm-thick, strong medium columnar,
loam, natric B2t horizon, an 8-cm-thick,
massive, loam B3 horizon, and a to-cmthick, white, very gravelly loam IICca horizon over shattered, carbonate-impregnated
bedrock. This soil has 22-26% CaCO:l
equivalent for its gravel-free solum, and is
saline in its B2t, B3, and IICca horizons. It
is afine-Ioamy, mixed, thermic, Lithic Natrargid. The soil of the younger Rainbow fan
surface is a coarse-loamy, mixed, thermic
Typic Torriorthent. The soil of the adjacent
playa is afine-loamy, mixed. thermic Typic
Torriorthent.
SOIL GENESIS
O.."...".<nt-'¢
o\~~oo~""':
8N
'£::
o
:I:
The pedogenic and illuvial nature of the
B2t horizon, and the pedogenic and eluvial
nature of the Av horizon are demonstrated
by several lines of evidence. Both horizons
approximately parallel the land surface;
variations in thickness and depth are related to probable fan-alluvium texture, as
previously described, and can be explained
by effective leaching depth.
The clay accumulated in the B2t uniformly coats and prominently reddens
skeletal sand grains; hence it has altered the
horizon. Where the alluvium was coarsesand textured, the thin clay coatings can be
seen bridging between sand grains in a
fashion discordant with the original fabric
of the alluvium. Clay deposition in the B3
horizon is in 1- to iO-mm-thick bands, or
lamellae, within which the sand grains are
coated and bridged by reddish-brown clay;
sand grains between lamellae are grayish
and clean. The lamellae both follow and cut
across fine alluvial stratification with angular discordance. Clay bridging and
lamellae are most prominent at the upper,
coarsest textured end of the fan skirt.
Illuvial and pedogenic clay lamellae are
common in sandy parent materials 10
humid regions (i.e., udic soil-moistureregime areas) (Dijkerman et al .. 1967). The
author has seen them frequently in xeric
soils and several times in aridic soils. In
these latter two cases, at least, lamellae are
the first morphological forms of illuvial clay
184
FREDERICK F. PETERSON
deposition in clean sands, in some sandy illuviation of the clay fraction. The ratios of
loams, and some low-clay, silt-loam parent both total and acid-insoluble silt to clay
materials. In relatively very young sedi- percentages in the A v and B2t horizons
ments the lamellae occur throughout the shows that not only does clay content in·
B-horizon depth zone: with continued clay crease, but it increases relative to silt con·
illuviation those in the upper part of this tent from the A v to B2t horizon. If dust had
zone are masked by overall illuvial clay infiltrated without some preferential clay
coating, but clay illuviation seems to cease eluviation, the ratio of silt to clay would
in the B3 position and the lamellae there are have remained constant.
preserved. When clay accumulation in the
Attributing the source of clay and silt to
B2 position is great enough for soil shrink· dust infiltration also helps explain the rela·
ing and swelling to create soil structure, tively great thickness and clay content of
lamellae are completely obscured.
the natric horizon when compared with relOn the middle and lower fan skirt, where atively thin A v horizon, which traditionally
clay accumulation has altered the texture of is considered the source of illuvial clay. (At
parent material from sandy loam to clay four sites along cut 6, other than the sample
loam, shrinking and swelling has created site, the B2t horizon is 1.7,3.6,7.0, and 4.0
weak to moderate, coarse prismatic or col- times as thick as the Av horizon: the B2t
umnar structure in the B2t horizon. In some horizon has somewhat more than twice the
places there even has been infiltration of percentage clay content as the A v horizon).
grayish A v·horizon material into the cracks Where dust fall and infiltration are active,
between the columnar peds. This soil an A horizon may act more nearly as a
structure is additional evidence of discor· transport zone for eolian clay, and some
dance, and of the pedogenic nature of the silt, than as a clay source. There is common
B2t horizon. Not only silicate clay, but also evidence of dust fall and infiltration in
carbonate clay, appears to have accumu· Nevada, New Mexico, and other desert
lated in the B2t horizon, relative to the Av areas (Peterson, 1977: Gile, 1975: Yaalon
horizon, since the proportion of carbonate and Ganor, 1973).
in the clay fraction is similar throughout the
Effective dispersion of the calcareous
solum. As significantly, hoth the Av and clays by sodium salts is suggested by very
B2t horizons are markedly finer textured turbid pools that collect in microdepres·
than the B3 horizon, or the sand or loamy sions at the periphery of the fan skirt after
sand C horizon of fan alluvium occurring heavy storms. Clay remains in suspension
below the B3 horizon over much of the for several days until the water evaporates.
soil's extent (cf., Fig. 3a). Since the fan al· The fan Natrargid is so saline (e.g .. the satluvium probably was originally a sand or uration extract of the Av horizon is 0.9 N;
loamy sand throughout (as seems reason· Table 3) that one might suspect salt floccu·
able for at least the upper fan) and since the lation would prevent clay dispersion and
materials are young and still highly calcare· eluviation. However, the soil samples were
ous, and have been subject to only the lim- collected from dry soil; surface salt
ited leaching of an arid environment, it does efflorescences in spots on the dry soil indinot seem reasonable that the silt and clay cate capillary salt movement to, and concontents of the solum are products of centration in, the surface soil as it dries.
chemical weathering. They may be attrib- During a storm, the Av horizon should be
uted to infiltration of eolian dust, either de· leached to some lower salt concentration
posited directly or washed from the hill and clay should disperse. As a qualitative
across the fan. The dispersive influence of test of clay flocculation by salts, Avsodium should have aided infiltration of horizon material was equilibrated by four
both silt and clay, and is hypothesized to centrifuge washings with 0.1, 0.2, 0.3. 0.4.
account for the preferential eluviation and 0.5, and 0.6 N NaCI. After the final cen-
HOLOCENE PLAYA-MARGIN SOILS
trifuging, which should have sedimented all
flocculated clay, all supernatants were still
somewhat turbid. The surface layer of apparently clayey sediment occupied at least
twice the volume, when equilibrated with
0.6 N NaCI, as its weight percentage would
suggest. The clayey sediment showed increased volume, or water imbibition against
centrifugal force, with decreasing salt concentration; in 0.1 N NaCl some four times
greater volume occurred than expected if
the clay were tightly flocculated. This
marked swelling suggests that under heavy
storms or sheetflood irrigation, at least
clayey aggregate spalling should occur in
this salty soil, thus releasing clay for eluviation.
Soluble-salt distribution suggests some
downward translocation and accumulation
in the lower B2t horizon, and perhaps a yet
earlier accumulation in the C horizon. Because the surficial playa sediments are
saline, the salt in the Natrargid solum probably accumulated along with the postulated
eolian silt and clay. Part of the salt, and
particularly the halite and gypsumcemented "Gm" lenses in the C horizon,
may have accumulated from saline
groundwater as the playa sediments were
being deposited. In either case, Na for clay
dispersion should have been present during
soil formation.
CONCLUSIONS
The Typic N atrargid of the Lake Hill
fan-skirt surface is pedogenic because clay
accumulation altering the parent alluvium
of its natric horizon is discordant with both
stratification and fabric of the alluvium, and
because the horizon parallels the land surface. Clay. and probably silt, illuviation has
occurred in very calcareous and saline parent material under an arid climate. Apparently both carbonate and silicate clay have
translocated under the dispersive influence
of sodium salts. The soil has formed in less
than about 10,000 yr as inferred by
radiocarbon dating at the site, or in less
than about 3500 yr by stratigraphic correlation to radiocarbon-dated sediment in the
185
adjacent Searles Lake basin, and probably
in less than about 2000 yr by correlation
with the period of deposition proposed for
the analogous Searles Lake sediment. The
dispersive sodium salts and clay for translocation probably were provided from the
adjacent playa by dust falL
The similar Haplargids, or non-sodiumaffected desert soils with a horizon of illuvial clay accumulation, most commonly are
late Pleistocene age or older and do not
form in still strongly calcareous parent materials. Natrargids, such as this one in
Panamint Valley, could be confused with
Haplargids only cursorily studied, and their
age and conditions of formation misinterpreted.
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