Geoderma, 28 (1982) 173-202
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
173
EVOLUTION OF REG SOILS IN SOUTHERN ISRAEL AND SINAI·
J. DAN', D.H. YAALON', R. MOSHE3 and S. NISSIM'
'Institute of Soils and Water, Volcani Center, Bet Dagan (Israel)
, Department of Geology, The Hebrew University of Jerusalem (Israel)
3 Division of Soil Conservation and Drainage, Ministry of Agriculture, Be 'er Sheva (Israel)
(Received October 26,1981; accepted March 1, 1982)
ABSTRACT
Dan, J., Yaalon, D.H., Moshe, R. and Nissim, S., 1982. Evolution of Reg soils in southern
Israel and Sinai. Geoderma, 28: 173-202.
Reg soils (mostly Camborthids and Gypsiorthids) cover some 15% of the Negev and
Sinai deserts. Analytical data of seven profiles on depositional surfaces of increasing age
in the Negev show clear relationships between ages of surfaces and soil profile features,
exemplified in the development of the cambic, salic and gypsic horizons.
The youngest soil, a Coarse Desert Alluvium soil (Typic Torriorthent) of dry wadi beds,
up to a few thousand years old, has little profile differentiation and is generally non-saline
or slightly saline. On the higher terraces connected with the Lisan Formation (about
70000-12000 years B.P.) clear profile differentiation and the beginning of development
of cambic horizons can be discerned, evident in their colour-textural differences. The soils
are already saline and somewhat gypsiferous. Both soils are not yet defined as Regs because of their negligible or restricted profile differentiation.
Reg soils on the older and higher geomorphic surfaces in the Arava Rift Valley, several
hundred thousand years old, have well-differentiated profiles, with cambic, salic and gypsic
horizons. Below their stony desert pavements, typical Reg soils have light coloured vesicular horizons, over mellow, very pale brown loam, frequently with laminar structure, almost completely stone·free layers. The reddish brown loamy to clay loam B horizons are
very saline and show intensive salt weathering of gravels. Gypsic and petrogypsic horizons
occur at depth. Such Reg soils represent the stable surfaces and soils of deserts and were
developed over a long period of desert weathering.
INTRODUCTION
Reg soils are the typical soils of the gravelly deserts of Israel (Ravikovitch
et al., 1956; Dan et al., 1981, chapters 2 and 11). In contrast to most other
desert soils, they exhibit soil horizons that are related to soil genesis. These
horizons include an upper, shallow, greyish vesicular horizon and a somewhat
deeper, yellowish red saline dusty layer (Ravikovitch et al., 1956; Dan et al.,
1981). The underlying parent material is usually reached at a depth of 0.5-1
meter. A well-developed desert pavement characterizes these soils. They are,
*Contribution from the Agricultural Research Organization, Israel, No. 182,1981 Series.
0016-7061/82/0000-0000/$02.75 © 1982 Elsevier Scientific Publishing Company
174
as a rule, saline and gypsiferous; some Regs are also characterized by petrogypsic horizons.
The Regs cover the large desert gravel plains in the Middle East, (Zohary,
1940; Moormann, 1959; Veenenbos and Ghaith, 1964; Dewan and Famouri,
1964; Dan and Raz, 1970) North Africa, and other extremely arid regions *1
of the world (D'Hoore, 1964). The typical Regs differ from the other semidesert or zonal desert soils such as the Grey, Grey brown, and Red desert
soils by the restricted depths of their horizons and their higher salt contents.
Most of the Regs may be correlated with the Orthids (Camborthids and Gypsiorthids) of the American Soil Taxonomy (Soil Survey Staff, 1975); however, many relatively young Regs may not be deep enough and thus they are
included among the Entisols (Torripsamments or Torriorthents).
The object of this paper is to present data of several profiles on a sequence
of depositional surfaces of increasing age and to discuss briefly the evolution
of the main pedogenetic horizons and features.
DESCRIPTION OF THE AREA
In Israel the Regs are confined to the extremely arid zone where the annual
rainfall does not usually exceed 65 mm (Dan and Raz, 1970; Dan, 1979;
Dan et al., 1981). They cover some 15% of the desert surface. The zone includes all of the Arava Valley, the southern Negev, and most of the Sinai
Peninsula. Three broad geographic-soil regions characterize these desert areas
(Dan, 1979, Fig. 1).
(1) The mO}lntainous zone (southern Sinai, some parts of central Sinai
and the slopes of the Negev mountains).
(2) The sandy areas (northern Sinai).
(3) The gravelly plruns and the large valleys (the Arava Valley and the
plains of Paran and the central Sinai).
Soil development in the first two geographic regions is restricted by severe
water or wind erosion (Dan, 1979; Dan et al., 1981). The gravelly plains, on
the other hand, are mostly flat and the gravel cover protects the soil from accelerated erosion (Ravikovitch et al., 1956; Dan and Raz, 1970). The surface
stability is such that soil development occurs, despite its slow rate.
Stones and gravel in the plains and valleys of southern Israel and Sinai
have been deposited since Neogene times (Bentor and Vroman, 1951, 1954,
1957; Horowitz, 1979). These stones and gravel consist usually of a mixture
of limestone, dolomite and flint fragments mixed with some fine soil material.
The relative proportions of the various stones are related mainly to the source
*1 Extremely arid regions are defined according to Meigs (1953) as areas where
the moisture index, defined by Thornthwaite, is less than -57. In Israel these include
mainly areas where the annual rainfall is less than 65 mm and where the vegetation is
restricted to favourable ecological sites which receive additional runon water from the surroundings.
175
L E &E I I
~
m=TI
Cd
~
MOU .. T.'N'
YOUNC
•• , .
VALLEYS
PL.,N . . . . . INly GRAVELLY PLAINS
SANDY."EA.
"""HERN .-DEII Of THE [lTIt(MEL Y
IOUTHEJtN ANO UI'EItN
MtiD
X
ARID ZON.:
_DEli Of THE
MILDLY
ZONE
IAlIIlI'UtrIQ IITU
IIEDITEUUEU
SEA
Fig. 1. Regional map of the arid parts of Israel and Sinai.
176
area and also to some extent to the distance of transportation. Flint gravel is
especially widespread near Campanian flint outcrops whereas dolomite and
limestone fragments are more widespread near mountains composed of
carbonate rocks. It should be stressed, however, that most of the stony and
gravelly sediments include at least some flint fragments due to the mixed
~
MOUNT SEDOM
LJ
DEAD SEA SURFACE
I.
LlSAN SURFACE
~-=-~I
I.J
~:~~o~oj
X
PLEISTOCENE
DEPOSITIONAL SURFACES
LATE NEOGENE
(ARAVA CONGLOMERATE)
SURFACE
ROAD
SAMPLING SITES
NEGEV
MOUNTAINS
o
JUDEAN
DESERT
EDOM
5
Fig. 2. Generalized map showing the various surfaces in the central and northern Arava
Valley.
177
nature of most of these formations or because of the occurrence of thin flint
beds among the carbonate rocks.
In many places several depositional surfaces can be detected. These depositional surfaces are clearly distinguished in the northern and central Arava
Valley, where most of the soil samples were collected (Figs. 2,3). These
various surfaces will be described briefly, due to the importance of relationships between their ages and the soil characteristics.
lISAN
DEAD SEA
..; GRAVEL. STONES
~x"::i
MARL
SURFACE
D=~~RLAYER
INTERMEDIATE
PLEISTOCENE
SURFACE
1.:t;:~~ISTRATIFlEO
ALLl.MJM
NEOGENE
EROSIONAL
SURFACE
NEOGENE
DEPOSITIONAL
SURFACE
~GYPSUM
CRUST
D
DESE"" NVEM[NT
Fig. 3. A schematic cross-section showing the relationships between soil profile characteristics and the various surfaces in the central and northern Arava Valley.
(1) The lowest depositional surface - The Dead Sea surface - is connected
with the Recent Dead Sea and the saline-alluvial sediments of Arvat Sedom
(the wet saline playa south of the Dead Sea). South of Arvat Sed om this
surface is confined to the Nahal HaArava wadi bed and to a small Recent terrace near the wadi. This surface rises in a gradient of about 1% to the vicinity
of En Yahav, where the wadi beds attain a more gentle gradient, and merge
with the higher surfaces.
(2) The second surface - The Lisan surface - is connected with the former
Lisan Lake or the Pleistocene Dead Sea. The lacustrine sediments of this
ancient lake merge and interfinger, in the vicinity of Hazeva, with the saline,
clayey, silty and sandy deposits of the ancient wet playa that bordered the
lake proper. Further south, these sediments merge and interfinger with gravelly sediments which cover the whole upper terrace of Nahal HaArava north of
En Yahav; in the settlement of En Yahav itself, the Lisan surface may be
correlated with the ancient saline gypsiferous salt-marsh sediments that surrounded a former spring; these sediments are found nowadays several meters
higher than the Recent springs and wadi beds. The depositional Lisan surface
continues south of En Yahav to the vicinity of Zofar where the wadi beds and
the lower terraces may be correlated with that surface.
178
(3) The third surface, or surfaces, are less uniform. Actually, they consist
of Pleistocene depositional surfaces composed of flat terraces, hilltops and
plains which may be detected in the vicinity of Hazeva between the Arava
Conglomerate (see below) at an elevation of -100 m near Hazeva and the
Lisan Lake surface at an elevation of -150 m in the same area. The ages of
these surfaces are not well-established, but it is evident that they were formed
during the Pleistocene, inasmuch as they are younger than the Arava Conglomerate which is related to the late Pliocene (Bentor and Vroman, 1957).
The regional distribution of these surfaces is not readily evident. The surfaces
are quite clear and widespread in the vicinity of Hazeva but they become more
diffuse southwards. In these areas the surfaces may merge gradually with the
older Arava Conglomerate surface.
(4) The oldest depositional surface, which is of great extent, is the Late
Neogene Arava Conglomerate surface, which may be covered by gravel of the
Meshar Formation (Horowitz, 1979). The Arava Conglomerate and the Meshar
Formations covered large areas in the past (Bentor and Vroman, 1951, 1954,
1957). In the vicinity of Hazeva they characterize the tops of small eroded
mesas (table mountains). The area of this surface and its sediments become
more continuous on the western edge of the Arava Valley. Toward the south,
the vertical distance between this surface and the younger ones diminishes
until it is negligible and reaches only a few meters in the central Arava. This
surface continues westward toward the plains of Paran and central Sinai
where they apparently include most of the higher gravelly plains of this
region (Horowitz, 1979; Dan et al., 1981). In these areas, however, this surface is again dissected due to relative uplift at the beginning of the Pleistocene
and some younger depositional surfaces and terraces may be found.
CLIMATE AND VEGETATION
The climate of the areas concerned is extremely arid and the moisture index is lower than -57 (Meigs, 1953). Temperatures may differ according to
elevation; the rainfall is very scarce and the annual average of most of the
area does not exceed 50 mm (Rosenan, 1970; Israel Meteorological Service,
1967). This figure has really very little meaning, however, because the yearly
variations are very large (Ganor et al., 1973). In a single severe thunderstorm
the rainfall may exceed the annual average.
The Reg plains are, as a rule, bare of vegetation (Zohary, 1955; Dan and
Raz, 1970). Vegetation is usually confined to the stream-beds, where the
plants take advantage of the runoff water that reaches these places. In exceptionally wet years, however, some scattered Mesambryanthemum plants
may be found in some of the Reg plains.
METHODS AND PROCEDURES
Seven soil profiles from several different depositional surfaces were sam-
179
pled. Three of these profiles were collected in the vicinity of Hazeva. The
first profile was sampled from the Recent Arava river terrace (the Dead Sea
surface), the second one from the somewhat higher gravelly terrace that is
connected with the Lisan marl sediments (the Lisan surface), and the third
one was sampled from a dissected higher terrace that is related to the intermediate Pleistocene surfaces. The samples of the profile that characterizes
the highest surface were taken from central Sinai; because near Hazeva this
surface is already eroded and dissected. The samples of profile nos. 5-7 were
collected from surfaces near Bir Thamada in central Sinai. Profile no. 5 characterizes the lower dry wadi bed, profile no. 6 an intermediate terrace, and
profile no. 7 the higher flat upland areas.
The soils were described in detail (according to the FAO system; FAO,
1968), sampled, and classified according to the Israeli and American systems
(Soil Survey Staff, 1975; Committee on Soil Classification in Israel, 1979).
The pH, electrical conductivity, features of the exchangeable complex, gypsum and soluble ions were analyzed according to the standard methods followed in the Salinity Laboratory at Riverside, California (Richards, 1954).
Lime content was determined by the calcimeter method and mechanical composition by the Beam method (Wright, 1939). Exchangeable Na and K were
determined in profiles 5-7 after removal of the soluble salts by alcohol. In
profiles 1-3 exchangeable potassium was determined from solution which
was gained due to removal of the K ions by ammonium acetate solution; in
profiles 4-7, the K ions were removed by sodium acetate solution.
,
PROFILE DESCRIPTIONS
Profile No.1 - Coarse Desert Alluvium
Location:
Site:
Profile description:
Cll 0-8 cm
1 km east of Hazeva, near Nahal HaArava wadi bank at
coordinate 1780/0196.
The pit was located on a young, Recent terrace, 50 m
west of the dry wadi bank. The terrace is only 1-2 m
higher than the wadi bed. The vegetation consisted
mainly of Haloxylon persicum and some Salsola shrubs.
Most of the vegetation was restricted to shallow depressions, where the rainwater usually concentrated. The
ground near the pit was bare of vegetation. The area
was nearly flat, with a small slope of 1 % eastwards. The
soil surface was covered by limestone and flint gravel.
Many limestone, flint and some quartz porphyry cobbles
and gravel were found also in the various soil layers.
Very pale brown (10YR 7/3) dry, light yellowish brown
(10YR 6/4) moist, gravelly and stony (about 20% gravel
180
C12 8-30 cm
C13 30-60 cm
C14 60-82 cm
C15 82-100 cm
and stones) sand; single grained, loose, non-sticky and
non-plastic; smooth, clear boundary.
Similar sand with only 1% gravel; clear alluvial layering;
smooth clear boundary.
Similar sand with a considerable amount of gravel
(about 20%) and stones; no clear alluvial layering;
smooth clear boundary.
Similar layer with much (about 70%) gravel and stones;
the sand among the stones was very coarse; smooth
clear boundary.
Similar layer with only 5% gravel, clear alluvial layering
and finer sand; the underlying layer is again more stony.
Profile No.2 - Young Regosolic Reg, a transition to Coarse Desert Alluvium
Location:
Site:
2 km north of En Yahav, at coordinate 1742/0106.
Pleistocene gravel terrace that interfingers with the upper sediments of the Lisan marl sediments further
northward. The area is flat, with a very small slope toward the northeast. The vegetation was restricted to
the dry wadi beds, and consisted mainly of Acacia tortilis and Anabasis articulata. Some other desert plants,
mainly Fagonia arabica, were also seen. The pit was
located on a bare surface, 10 m from the nearby dry
wadi bed. The soil was covered by flint and limestone
gravel. A few stones were also found in the area. Distinct desert varnish stains this gravel. The whole soil is
gravelly and highly calcareous. The gravel in the various
soil layers consist mainly of limestone fragments with
admixture of about 30% flint.
Profile description:
Ao
A
0-lcm
B
1-4cm
Clcs
4-15 cm
C2
15-70 cm
Superficial cover of gravel with desert varnish.
Very pale brown (10YR 7/3) dry, light yellowish brown
(10YR 6/4) moist, sandy loam; vesicular structure; soft,
non-sticky but slightly plastic; smooth, clear boundary.
Reddish yellow (7.5YR 6/6) dry, reddish yellow to
strong brown (7.5YR 5.5/6) moist, slightly gravelly
(10% gravel) loamy sand; massive, soft, non-sticky but
slightly plastic; smooth clear boundary.
Very pale brown (10YR 7.5/3 dry, 10 YR 7/4 moist)
gravelly (50% gravel) sand with a few scattered gypsum
crystals and some disintegrating stones; single grained,
loose, non-sticky and non-plastic; gradual boundary.
Similar layer without gypsum crystals; the deeper layer
(beyond 50 cm) was less gravelly (only 30% gravel).
181
Profile No.3 - Petrogypsic Regosolic Reg
Location:
Site:
1 km southeast of Hazeva, at coordinate 1758/0182.
The profile was sampled on a dissected Pleistocene terrace. The whole area is already somewhat hilly, but
flat areas about 20-40 m wide still characterize the water divides. The soil was sampled on a typical flat hilltop. The terrace is 10-15 m above the wadi beds and
lower plain that are connected with the Lisan surface.
The flat areas were bare of vegetation. Some scattered small shrubs of Anabasis articulata and Zygophyllum dumosum were found along the dry small wadi beds
on the terrace slopes. The vegetation of the dry wadi
beds in the lower plain consisted of the Acacia tortilisAnabasis articulata plant association.
The soil surface was covered by flint gravel with a
distinct coating of desert varnish; few limestone and
quartz porphyry gravel were also found. Stones and
gravel were found in the various soil horizons although
the relative proportions of limestone gravel increased in
the deeper soil layers. The whole soil profile was highly
calcareous.
Profile description:
Ao
A
0---1 cm
B21sa
1-5 cm
B22cs
5-12 cm
B3sa
12-20 cm
Cllsacs
20-39 cm
C12
39-52 cm
Superficial cover of flint gravel with desert varnish.
Very pale brown (10YR 7/3) dry, light yellowish brown
(10YR 6/4) moist, slightly gravelly, fine sandy loam;
vesicular structure; soft, non-sticky but slightly plastic;
smooth clear boundary.
Reddish yellow (7.5YR 6/6) dry, strong brown (7.5YR
5/6) moist, very saline gravelly (about 20% gravel) loam
to clay loam; loose, sticky and plastic; wavy clear
boundary.
A layer of white dusty gypsum of very low density concentrated mainly in large chunks; somewhat gravelly;
wavy clear boundary.
Light brown to light yellowish brown (9YR 6/4) dry,
strong brown (7.5YR 5/6) moist, gravelly (30% gravel)
loam to sandy loam with many white mottles of gypsum
and salt crystals; loose, slightly sticky and slightly
plastic; clear to gradual boundary.
White (10YR 8/1) dry, very pale brown (10YR 7/3)
moist, massive, gravelly (30% gravel) loamy sand to
sandy loamy layer indurated by gypsum; extremely
hard, non-sticky and non-plastic; gradual boundary.
Very pale brown (10YR 7/3) dry, very pale brown to
182
light yellowish brown (10YR 6.5/4) moist, very gravelly
(50% gravel) sand with many gypsum crystals; massive,
soft, non-sticky and non-plastic; clear to gradual boundary,
C13cs 52-100 cm Similar to above layer, with more gypsum crystals that
indurate part of the layer; clear boundary.
C14
100--117 cm Similar to above layer with fewer gypsum crystals that
diminish with increasing depth; gradual boundary.
C2
117-135 cm Similar to above layer with very few gypsum crystals.
Profile No.4 - Deep Regosolic Reg (Fig. 4)
Location:
Site:
Profile description:
Ao
0-3 cm
All
A12
B1
B2cs
B3sacs
C11cs
Central Sinai, 35 km southeast of Qal'at en Nakhl.
The profile was sampled on an old, somewhat dissected
gravel plateau. The area was flat. The soil was covered
by flint gravel with distinct coating of desert varnish.
The surface was bare of vegetation.
A complete cover of flint gravel with desert varnish.
Very pale brown (10YR 7/3) dry, yellowish brown (10YR
5/5) moist, sandy loam; vesicular structure; slightly
hard, non-sticky but slightly plastic; smooth, clear
boundary.
3-9 cm
Very pale brown (10YR 7/3) dry, light yellowish brown
(10YR 6/4) moist, slightly gravelly loamy sand, with
some small white mottles; massive to laminar structure;
slightly hard, non-sticky but slightly plastic; smooth
clear boundary.
9-19 cm Strong brown (7.5YR 5/6) dry and moist, slightly
gravelly sandy clay loam; columnar structure; the column margins are pale brown, massive and sandy and the
insides are strong brown, loose and loamy; slightly hard,
non-sticky and non-plastic at the column margins and
loose, slightly sticky and plastic inside the columns;
diffuse boundary.
19-35 cm Strong brown (7.5YR 5/6) dry and moist, gravelly
sandy loam (about 30% gravel); many disintegrating
stones; loose, slightly sticky and plastic; wavy, clear
boundary.
35-47 cm Light brown (7.5YR 6/4) dry, strong brown (7.5YR
5/6) moist, gravelly (50% gravel) sandy loam; massive
layer indurated somewhat by gypsum; wavy, clear
boundary.
47-100 cm Very pale brown (10YR 8/3) dry, light yellowish-brown
(10YR 6/4) moist, massive layer indurated by gypsum;
part of this induration is in a vesicular form; gradual
boundary.
183
Fig. 4. Typical profile of a deep regosolic Reg (profile No.4).
C12cs 100-110 cm Similar to above layer with vesicular gypsum induration
that decreases gradually with depth; gradual boundary.
C13
110-120 cm Very pale brown (9YR 8/4 dry, 9YR 7/4 moist) loose
gravelly loamy sand with some gypsum crystals that
decrease with depth; single-grained, loose, non-sticky and
non-plastic; gradual boundary.
C2
120-130 cm Similar to above layer without gypsum crystals.
Profile No.5 - Coarse Desert Alluvium
Location:
Site:
1 km north of the road junction near Bir-eth Thamada
in Central Sinai at coordinate 54365/33940.
The pit was in a dry broad (300 m wide) wadi bed between the stream beds where the vegetation is concentrated; the distance to the nearest plant is 10 m. Some
small scattered shrubs of Zygophyllum dumosum were
found in the wadi bed. The area was flat and limestone
gravel covered the soil surface. The gravel in the various
soil layers consist also of limestone fragments.
184
Profile description:
0-10 cm
A
AC 10-24 cm
C11 24-40 cm
C12 40-56 cm
C13 56-110 cm
Very pale brown (10YR 7/4) dry, light yellowish brown
(10YR 6/4) moist, very gravelly (about 50% gravel)
loamy sand to sandy loam; weak fine subangular blocky
structure; loose to soft, non-sticky and non-plastic;
clear boundary.
Similar to above layer but only slightly gravelly (about
10% gravel) and sandy loam texture; clear boundary.
Similar to above layer but very gravelly (about 70%
gravel) sand to loamy sand texture without any structure and loose consistency in dry conditions; clear
boundary.
Similar to above layer but only slightly gravelly (about
10% gravel) and sandy texture; clear boundary.
Similar to above layer but very gravelly (about 6070% gravel).
Profile No.6 -- Young Regosolic Reg
Location:
Site:
Profile description:
Ao
A
0-4cm
B2sa
B3cs
200 m north of profile 7 and 150 m south of profile 5
near Bir-eth Thamada in central Sinai, at coordinate
54338/33914.
The soil is on a terrace about 20 m from the terrace
escarpment. The area is flat, and the soil is covered by
a desert pavement consisting of flint and limestone
gravel that are coated by a distinct desert varnish. This
pavement covers about 50% of the ground. The gravel
found in the various soil layers, especially in the deeper
ones, consist mainly of limestone fragments. The soil
is bare of vegetation. The whole profile is highly calcareous.
Superficial cover of gravel with desert varnish.
Very pale brown (10YR 7/4) dry, yellowish brown
(10YR 5/6) moist, slightly gravelly (10% gravel) sandy
loam; vesicular structure; soft to slightly hard, nonsticky but slightly plastic; some narrow cracks, 5 cm
apart, were seen in this layer; wavy clear boundary.
4-15 cm Reddish yellow (7.5YR 6/6) dry, strong brown (7.5YR
4/6) moist, slightly gravelly (about 10% gravel) loam to
sandy clay loam with common (10-20%) fine distinct
white mottles and some disintegrating stones; loose,
sticky and plastic; some penetration of A horizon materials occurs beneath the cracks; gradual boundary.
15-22 cm Reddish yellow (7.5YR 6/6) dry, strong brown (7.5YR
5/6) moist, gravelly (about 20% gravel) sandy loam with
185
many (about 30%) fine distinct white mottles (apparently gypsum); loose, slightly sticky and slightly plastic;
wavy, clear boundary.
Cllsacs 22-34 cm Reddish yellow (7.5YR 6/6) dry, strong brown (7.5YR
5/6) moist, gravelly (about 40% gravel), coarse sandy
loam with many (about 30%) fine distinct white mottles
(apparently partly gypsum); loose, slightly sticky and
slightly plastic; gradual boundary.
C12cs 34--78 cm Light yellowish brown (10YR 6/4) dry, yellowish brown
(10YR 5/4) moist, very gravelly (about 60% gravel),
slightly indurated sand; some parts of this horizon are
more indurated while others are less; the induration is
caused by gypsum; massive, slightly hard, non-sticky
and non-plastic; gradual boundary.
C13
78-130 cm Light yellowish brown (10YR 6/4) dry, yellowish brown
(10YR 5/4) moist, very gravelly (about 30% gravel)
coarse sand; some gypsum crystals were seen; single
grained, loose, non-sticky and non-plastic; gradual
boundary.
C2
130-150 cm Similar to above layer without gypsum crystals.
Profile No. 7 - Mature Regosolic Reg
Location:
Site:
Profile description:
Ao
A
O---7cm
B2sa
7-16 cm
200 m south of profile 6, near Bir-eth Thamada in
central Sinai, at coordinate 54305/33888.
The soil characterizes the upper part of the plain. The
area is flat, with a westward slope of 1.5%. The soil was
paved by flint and limestone gravel that covers about
50% of the ground surface. Distinct desert varnish
covered this gravel. The relative amount of flint gravel
decreases with depth and from 25 cm downwards only
few flint fragments were visible. The soil is bare of
vegetation. All the soil is highly calcareous. The pit was
about 50 m from the escarpment to a lower terrace.
A complete cover of flint gravel with strong desert varnish.
Light yellowish brown (10YR 6/4) dry, yellowish brown
(10YR 5/4) moist, sandy loam; vesicular structure; soft
to slightly hard, non-sticky but slightly plastic; some
very small cracks about 5-10 cm apart; wavy clear
boundary.
Yellowish red (5YR 4/5) dry and moist, gravelly (30%
gravel) saline clay loam with numerous small white
mottles; loose, sticky and plastic; some intrusions of A
horizon materials are underneath the small cracks to
a depth of 15 cm; clear boundary.
186
B3sa
16-25 cm
Yellowish red (6YR 5/6 dry, 5YR 5/6 moist) gravelly
(30% gravel) saline loam to clay loam; loose, sticky and
plastic; clear boundary.
BCsa 25-39 cm
Pink (7.5YR 7/4) dry, reddish-yellow (7.5YR 6/6)
moist, very gravelly (about 50% gravel) sandy loam;
loose, slightly sticky and slightly plastic; clear boundary.
Cllsa 39-50 cm
Very pale brown (10YR 7/3) dry, yellowish brown to
brownish yellow (10YR 6/5) moist, very gravelly
(50-60% gravel) loamy sand to sandy loam; single
grained, loose, non-sticky and non-plastic; clear boundary.
Similar to above layer but more gravelly (60--70%
C12cs 50-80 cm
gravel) somewhat indurated by gypsum; clear boundary.
80-95 cm
Pink (7.5YR 7/4) dry, reddish yellow (7.5YR 6/6)
C13
moist, very gravelly (50--60% gravel) sand; single
grained, loose, non-sticky and non-plastic; clear boundary.
C14
95-120 cm Strong brown (7.5YR 5/6) dry and moist, very gravelly
(60% gravel), slightly indurated sandy loam; massive,
hard, non-sticky but slightly plastic.
Analytical data
The analytical data are presented in Tables I and II. Table I shows pH, the
amounts of gypsum and lime, CEC and the amount of exchangeable sodium
and potassium as well as the particle-size distribution. In Table II electrical
conductivity and values of the soluble anions and cations are presented.
TABLE I
Analytical results of pH, gypsum, carbonate, CEC, exchangeable Na and K, and mechanical
composition
Profile Depth
(cm)
and
horizon
Gypsum
Carbonates Cation
Exchangeable cations
pH of
(meq./100 g soil)
saturated CaSO."2H , O as CaC0 3 exchange
(%)
(%)
paste
capacity
K
Na
(meq./100 g)
Profile 1
C11
C12
C13
C14
C15
0-8
8-30
30-60
60-82
82-100
8.15
7.60
8.05
7.90
8.35
0.077
0.21
0.34
0.12
0.13
30.8
24.5
20.3
19.4
8.4
5.87
4.56
2.72
3.26
1.74
1.20
1.55
0.85
1.05
0.55
0.75
0.79
0.31
0.36
0.22
7.65
7.60
7.65
7.50
0.01
0.017
0.075
0.83
33.6
39.5
51.0
45.1
6.20
7.17
2.72
2.39
0.95
0.80
0.65
0.70
1.0
1.0
0.38
0.45
Profile 2
A
B
Clcs
C21
0-1
1-4
4-15
15- ·30
187
DISCUSSION
Formation of desert pavement
Soil formation in the extremely arid zone is restricted to areas that are
stabilized and protected from erosion (Fig. 5). The erosion in the desert is
generally severe because of the absence of a protective cover of vegetation
Fig. 5. A typical desert pavement of Reg soils.
Size class of particle diameter (mm)
Water content (%)
clay
<0.002
silt
0.002-0.05
fine sand
0.05-0.25
coarse sand
0.25-2
(%)
(%)
(%)
(%)
23.5
11.0
1.4
3.8
1.7
42.4
34.3
20.7
23.6
8.4
30.7
53.2
77.9
70.6
89.1
18.3
20.5
23.8
22.3
27.5
27.2
22.4
3.8
3.3
40.5
24.8
16.7
26.3
25.9
46.2
79.5
69.2
25.5
25.0
22.0
23.5
3.4
1.6
2.1
0.8
6.4
6.6
1.2
at saturation
air-dry
188
TABLE I (continued)
Profile Depth
(cm)
and
horizon
C22
C23
30-50
50-75
Gypsum
pH of
saturated CaSO. c 2H 2 O
(%)
paste
Carbonates Cation
Exchangeable cations
as CaC0 3 exchange
(meq./100 g soil)
(%)
capacity
(meq./100 g) Na
K
7.55
7.45
44.2
42.5
2.17
2.39
0.80
0.85
0.47
0.51
27.4
33.6
36.0
23.9
14.7
14.2
8.8
13.8
13.9
8.04
9.88
3.93
4.61
4.46
3.55
3.87
2.29
2.39
3.90
1.71
3.25*
9.32*
21.65*
8.09*
4.56*
4.89*
10.30*
0.92
0.83
0.38
0.39
0.31
0.29
0.29
0.28
0.24
10.59
8.63
8.94
10.43
9.17
4.41
4.68
4.69
4.87
2.9*
-*
2.9*
-*
-*
3.1*
-*
6.6*
4.3*
0.88
0.45
0.41
0.33
0.27
Tr
Tr
Tr
Tr
24.1
21.6
34.4
37.0
42.9
4.20
3.94
2.19
2.37
2.28
1.04
0.99
0.60
0.60
0.71
0.49
0.45
0.19
0.20
0.15
0.23
0.01
Profile 3
0-,1
7.50
A
1-5
B21sa
7.30
5-12 7.85
B22cs
12-20 7.40
B3sa
C11sacs 20-39 7.10
C12
39-52 7.60
52-100 7.77
C13cs
100-117 7.65
C14
117-135 7.75
C2
0.9
0.2
29.2
8.1
20.7
8.0
9.9
7.7
3.1
Profile 4
All
A12
B1
B2cs
B3sacs
C11cs
C11cs
C12cs
C13
0-3
3-9
9-19
19-35
35-47
47-75
75-100
10D-110
110-120
7.81
7.42
7.35
7.34
7.24
7.77
7.75
7.71
7.66
0.07
0.78
0.72
13.35
9.30
42.96
29.36
32.55
19.80
Profile 5
0-10
10-24
24-40
40-56
56--110
Profile 6
0-4
A
4-15
B2sa
B3cs
15-22
C11sacs 22-34
34-78
CI2cs
78-130
CI3
13D-150
C2
A
AC
C11
C12
C13
7.90
7.80
8.02
8.18
8.21
0.004
0.009
0.23
0.06
0.27
7.80
7.67
7.65
7.51
7.80
7.77
8.00
0.16
1.35
18.8
21.4
4.90
2.71
0.29
28.9
31.1
24.8
20.1
40.0
47.6
60.7
14.06
10.15
8.98
10.38
4.88
7.64
4.12
4.64
2.63
2.20
7.31
1.55
1.55
1.53
0.96
0.42
0.24
0.27
0.16
0.15
0.065
7.95
7.53
7.53
7.45
7.50
7.76
7.78
7.75
0.03
0.30
1.21
6.17
10.17
15.67
8.13
1.46
27.1
34.9
44.5
63.4
66.0
57.6
66.4
59.9
11.13
15.76
12.40
8.07
6.12
5.78
4.45
5.71
3.43
3.13
2.39
5.65
3.51
2.89
1.67
1.79
0.83
0.55
0.36
0.15
0.09
0.05
0.03
0.10
Profile 7
A
B2sa
B3sa
BCsa
C11sa
C12cs
C13
C14
0-7
7-16
16-25
25-39
39-50
50--80
8D-95
95-120
*The exchangeable sodium values are meaningless due to the high salt content; **the
high clay values include a large portion of gypsum.
189
Water content (%)
Size class of particle diameter (mm)
clay
<0.002
silt
0.002-0.05
(%)
(%)
air-dry
fine sand
0.05-0.25
(%)
coarse sand
0.25-2
(%)
at saturation
1.3
4.7
12.3
28.3
84.8
66.4
22.5
23.0
9.3
6.4
18.4**
4.3
18.8**
1.5
14.3**
0.8
2.2
43.7
43.6
23.7
12.5
13.8
6.1
11.0
4.8
2.2
29.7
30.4
34.6
28.3
16.3
23.6
12.1
14.6
21.1
17.3
19.6
23.2
44.9
51.1
68.9
62.7
79.8
74.5
28.7
24.5
50.0
25.3
30.5
31.0
39.9
29.9
25.0
11.4
6.0
5.6
11.7**
22.2**
36.6
25.9
20.6
21.8
35.9
50.9
64.6
66.5
54.0
27.8
1.6
2.9
7.4
12.5
14.0
35.8
30.4
33.6
43.3
37.4
63.6
43.5
47.9
36.0
1.9
1.9
2.0
1.2
1.4
9.9
7.2
2.2
3.3
3.0
59.8
49.7
20.0
48.7
16.8
28.4
41.2
75.8
46.7
78.9
20.6
22.4
21.6
27.3
22.0
0.8
1.1
0.6
0.8
0.6
21.1
9.0
17.8
22.8
9.4
8.0
3.6
22.8
20.9
7.8
12.8
2.6
7.4
2.7
36.6
32.4
45.8
27.9
33.3
15.9
7.6
19.5
37.8
28.6
36.6
54.7
68.7
86.2
33.2
26.2
39.5
39.1
28.9
33.9
27.1
3.4
3.7
6.6
8.4
2.6
2.8
1.1
14.3
4.2
13.2
17.0
15.3**
22.0**
9.6
11.4
14.4
42.5
21.9
24.2
21.9
17.4
14.8
11.0
53.6
31.4
23.0
20.1
16.0
13.0
16.3
14.4
17.2
22.0
41.8
38.6
46.8
47.6
59.4
63.2
30.3
38.3
38.9
31.1
33.8
36.8
29.2
38.2
2.4
4.6
5.1
3.8
4.5
5.9
2.4
2.4
1.6
0.6
0.8
6.1
1.3
2.3
1.7
4.5
0.9
......
co
o
TABLE II
Analytical results of the salinity contents and the features of the soluble ions
Profile Depth
and
(cm)
horizon
Profile 1:
0-8
C11
8-30
C12
C13
30--60
C14
60--82
82-100
C15
Profile 2:
0-1
A
1-4
B
4-15
C1cs
15-30
C21
C22
30--50
50-75
C23
Profile 3:
0-1
A
1-5
B21sa
B22cs
5-12
12-20
B3sa
C11sacs 20-39
39-52
C12
52-100
C13cs
100-117
C14
117-135
C2
Electrical
conductivity
(mmho/cm)
ESP
Water extract from saturated paste (meq./100 g soil)
Ca
Mg
Na
K
HC0 3
5.5
16.4
11.0
16.2
14.7
0.07
1.41
1.16
1.60
0.52
0.05
0.52
0.41
0.73
0.25
0.75
2.36
1.76
2.42
3.59
0.02
0.10
0.03
0.03
0.006
0.054
0.051
0.054
0.051
0.069
8.3
16.8
19.1
48.0
44.6
50.5
1.23
2.67
3.12
6.70
5.28
5.77
0.40
0.99
0.92
2.24
1.80
2.54
1.11
1.63
1.91
9.0
8.3
10.0
0.09
0.10
0.06
0.17
0.19
0.25
0.04
0.03
0.03
0.04
0.03
0.04
41.2
54.9
12.9
86.5
171.6
63.1
37.0
48.0
72.7
6.43
12.25
4.18
12.88
10.40
8.93
7.21
5.90
2.93
1.61
3.91
1.07
4.04
2.61
2.14
2.04
1.97
0.62
9.0
8.2
3.97
22.0
66.3
13.5
12.1
13.0
23.9
0.12
0.10
0.05
0.06
0.07
0.06
0.06
0.06
0.04
0.03
0.03
0.06
0.04
0.04
0.06
0.05
0.03
0.03
CI
SAR
SO.
0.98
2.82
2.02
2.90
3.99
1.52
1.29
1.83
0.30
20.4
34.0
31.3
32.2
31.6
23.5
16.8
12.9
15.0
34.9
1.79
3.63
5.39
13.90
11.93
14.38
1.00
1.73
0.59
4.68
3.60
4.14
15.3
11.2
23.9
29.3
36.9
35.6
7.7
7.6
9.1
27.8
29.4
32.4
3.73
7.28
3.71
8.98
48.5
17.3
82.7
?
?
?
?
?
?
26.5
18.4
11.0
47.5
149.0
32.0
28.2
37.9
113.5
13.4
17.2
5.5
30.0
114.4
21.6
17.2
18.5
26.2
2.94
4.20
2.35
1.31
Profile 4:
All
0-3
3-9
A12
B1
9-19
B2es
19-35
35-47
B3saes
47-75
C11es
75-100
C11es
C12es 100-100
C13
110-120
Profile 5:
0-10
A
AC
10-24
24-40
C11
40-56
C12
56-110
C13
Profile 6:
0-4
A
4-15
B2sa
15-22
B3es
C11saes 22-34
34-78
C12es
78-130
C13
C2
130-150
Profile 7:
A
0-7
7-16
B2sa
16-25
B3sa
BCsa
25-39
C11sa
39-50
C12es
50-80
C13
80-95
95-120
C14
?
89.1
0.70
1.81
1.26
1.11
1.00
24.8
25.1
27.4
25.3
31.1
8.7
22.7
10.8
8.6
8.1
12.45
14.75
18.25
35,21
11.20
9.50
4.34
4.25
4.29
3.90
3.65
3.58
2.88
2.11
33.0
25.9
24.5
70.4
31.8
20.3
37.1
30.5
30.2
24.6
44.2
26.3
17.3
13.9
3.72
22.96
25.3
32.63
22.41
14.71
9.90
14.31
1.67
2.47
4.82
4.57
2.55
2.28
30.8
19.9
19.3
70.0
57.4
50.0
37.5
31.4
16.8
19.0
17.4
43.1
24.2
22.6
20.0
16.1
0.09
0.08
0.07
0.09
0.10
0.13
0.10
0.10
0.08
2.34
11.8
17.4
50.4
134.5
11.6
23.1
22.2
22.0
0.92
4.49
1.60
0.45
1.08
0.05
0.12
0.05
0.06
0.04
0.05
0.06
0.05
0.06
0.06
1.29
6.26
2.37
2.39
1.65
3.06
2.98
3.38
4.81
2.41
2.59
1.54
10.10
10.26
11.73
23.92
8.17
5.80
3.02
0.07
0.04
0.05
0.06
0.03
0.03
0.02
0.08
0.06
0.13
0.12
0.08
0.10
0.07
1.14
4.43
6.31
4.23
3.56
2.36
3.13
10.26
10.71
21.40
11.56
8.80
5.08
7.05
0.04
0.05
0.05
0.04
0.03
0.03
0.02
0.02
0.07
0.10
0.09
0.09
0.09
0.08
0.07
0.10
0.78
7.96
14.2
23.3
18.8
6.9
7.6
7.8
7.9
0.38
4.5
3.7
7.2
5.3
3.4
3.9
3.5
4.3
10.9
39.1
18.9
14.6
14.0
0.85
2.12
1.31
0.93
0.99
0.21
1.39
0.72
1.13
0.63
47.9
69.4
60.2
96.9
26.2
19.4
12.5
3.55
5.82
8.13
10.19
4.26
4.06
1.94
10.0
35.1
38.5
55.4
38.6
26.5
22.8
23.9
1.15
10.79
13.13
11.62
9.90
5.90
5.40
6.11
3.93
2.5
5.8
7.6
43.1
142.4
11.9
21.3
19.1
18.0
17.6
13.4
13.9
53.0
211.4
16.1
42.5
36.6
38.5
0.05
0.03
0.02
0.03
0.02
0.01
0.01
0.01
0.01
9.4
34.9
46.0
86.3
182.6
24.6
48.1
44.0
51.8
1.3
6.4
8.1
23.2
32.0
10.5
9.6
8.1
8.1
2.71
27.4
31.9
70.3
......
(0
......
192
(Dan et al., 1981). Thus erosion is mainly due to the high water runoff in
the desert areas during the occasional rainstorms as a result of the low permeability of desert soils (Sharon, 1962; Hunt and Mabey, 1966; Cooke, 1970;
Shanan, 1975). Wind deflation may also occur, however, mainly in areas
which are not protected by a surface crust and where the surface layer is loose;
this happens usually on sandy sites (Dan et aI., 1981, chapter 2).
The erosion continues rapidly on the various desert landscapes until some
kind of gravel or stone protection is concentrated on the surface. This gravel
accumulates either because of erosion of the finer materials (Cooke, 1970)
or as a result of upward pushing of stones because of soil swelling and shrinking (Springer, 1958; Jessup, 1960; Mabbutt, 1965). It seems that in Israel
the formation of the desert pavement is partly due to erosion. It is likely,
however, that some upward movement of stones occurs in the well-differentiated Regs (profiles 4 and 7) in which the clay content of the A and B
horizons is relatively high and in which the high salinity may enhance this
process. The relative proportion of the unweatherable flint gravel increases in
the desert pavement of the well-differentiated Reg soils and in some of them,
especially in the Arava valley and the plains of Paran and most of central
Sinai (Dan et al., 1981, see profiles 3 and 4), no other stones or gravel are
found in this layer. The relative proportions of limestone and other carbonate
stones increase in the deeper soil layers and in some profiles, such as those
near Bir-eth Thamada, they comprise the absolute bulk majority of these
fragments. These stones and gravel disintegrate during the process of salt
weathering. Some of this weathered material may be eroded later, thus leaving
a concentration of the unweatherable flint gravel on the surface.
The sizes of the pavement gravel and stones in the pavement decrease
somewhat with time; in young soils some stones are found among the gravelly
pavements (see profile No.2) whereas in the older soils the pavement consists
entirely of small gravel. This phenomenon also characterizes similar desert
pavements in other countries (Hunt and Mabey, 1966; Cooke, 1970).
The disintegration of stones to gravel, both on the surface and in the
various soil layers, is affected to a large extent by salt crystal growth (Yaalon,
1970; Goudie, 1974). Insolation may also affect the splitting of gravel on the
surface (Peel, 1974).
The gravel that covers the soil is characterized by a desert varnish (Hunt
and Mabey, 1966; Cooke, 1970; Evenari et al., 1974; Dan et al., 1981; Dorn
and Oberlander, 1981). This varnish develops relatively fast (a few thousand
years) as it characterizes also the young Reg soils; it is missing only in the very
young coarse desert Alluvium which is found in stream beds. This varnish helps
to keep to a large extent the gravel from further disintegration due to the hardness of this layer; this seems true especially for limestone and dolomite fragments
as the flint gravel is already very hard and resistant to weathering.
193
Weathering and formation of mature soil horizons
The typical Reg soil has two thin well-differentiated horizons that may be con·
sidered as A and B horizons. The upper horizon always consists of a lightcoloured, somewhat loamy, vesicular layer (Evenari et al., 1974) that may be
designated as an A horizon. The lower part of it may have a laminar structure.
The underlying horizon, as a rule, consists of a mellow, loose yellowish red
or strong brown saline loam or even clay loam and is thus a cambic or argillic
horizon. The depths of these horizons are usually restricted to several centimeters. It seems that the depths of these horizons, their relative clay contents
and their distinctness may serve as criteria of Reg soil development.
The formation of soil horizons in the Regs is very slow. The youngest soil
(profiles 1 and 5) does not yet have any horizon and the clay content is
nearly nil and seems related to the alluvial parent material. Horizon differentiation of the somewhat older soil from the Lisan surface (profile 2) is also
very restricted. This soil exhibits only a very shallow vesicular A horizon and
the beginnings of a B horizon evident from the colour difference. The clay
content of these two shallow layers is also very low and does not exceed
6-7%. Horizon formation in the other soils is already clearly evident. The
upper horizons of profiles 3 and 6 are quite well differentiated. The total
depths of the upper two horizons, however, do not exceed 20 cm in profile
3 but are somewhat deeper in profile 6. Profiles 4 and 7 represent well-differentiated Reg soils in which the various horizons reach what seems to be
their maximum development. This stage is best expressed in profile 4. Very
few Reg soils reach this stage in the Negev (Ravikovitch et al., 1956).
The weathering and formation of the A and B horizon can occur only
when the soil is moist; the upper few centimeters may be moistened several
times during the winter months so that the formation of a shallow A and B
horizon as in profile 2 is relatively fast. Moisture penetration to greater depths
happens rarely and as a result a long time may pass before horizon differentiation may be marked in these layers. The maximum depth of water penetration in deep Reg soils reaches 50-60 cm (Gerson and Amit, 1982) but this
occurs very rarely; therefore a very long time may pass before these relatively
deep layers are weathered. Weathering to these depths (50-60 cm) is expressed only in the mature and old Reg soils of profiles 4 and 7. The high
salt content of the deep Reg soils enhances the deep weathering because
these layers remain moist for a relatively long time after the rainstorms due
to the hygroscopic nature of these salts.
Salinization
The various Reg soils have been gradually salinized by airborne salts
(Yaalon, 1963). These salts concentrate in the soil profile due to the restricted water penetration. The yearly addition of salt is small (Yaalon, 1964b)
but these salts are gradually concentrated.
194
Tr~
differences in salt contents of the various soils are significant. The
soil (profiles 1 and 5) is only slightly saline; the salinization increases in profile 2 and reaches maxima in profiles 3 and 4 (Fig. 6). Profiles
6 and 7 are also very saline, although the salinity values are lower than in
profiles 3 and 4 (Fig. 7). Chlorides of Na and gypsum are the main soluble
salts. Large amounts of CaCl 2 and MgCl 2 are also present.
Differential salt distribution characterizes these soil profiles. The differences are related to the limited wetting of the soils and the limited mobilization of salts under dry conditions (Yaalon, 1964a). The uppermost layers of
1 or 2 cm contain relatively small amounts of soluble salts. The salt content
increases in the next deeper layers (see Figs. 6 and 7). These layers (profile
2: 1-50 cm; profile 3: 1-20 cm; profile 4: 9--35 cm; profile 6: 4-22 cm;
and profile 7: 7-25 cm) are already very saline. The main salts include various
chlorides, among which are Ca and Mg chlorides, although in the upper parts
of these layers in profile 2 (1-15 cm) the amounts of Ca and Mg chlorides
are restricted. Gypsum is generally present and most profiles already have
considerable increases in the gypsum content in one of these layers (profile
2: 15-30 cm; profile 3: 5-12 em; profile 4: 2-9 cm; profile 6: 15-22 cm);
in profile 3 this increase is most significant and reaches very high values.
Nowadays, the gypsum seems to concentrate in this layer due to the very
low leaching activity of the rainwater.
The most saline layer is found somewhat deeper (profile 2: 50-75 cm;
profile 3: 20-39 cm; profile 4: 35-47 cm; profile 6: 22-34 cm; profile 7:
25-39 cm). The values of the salt contents in these layers in the older profiles
are extremely high. This is probably the deepest layer that is still reached by
the rainwater after the heaviest rainfall, as most of the salts are not leached
further downward. The depths of this layer in profiles 3, 4, 6 and 7 are more
or less the same, an argument that supports this hypothesis. In the younger
profiles this layer is found somewhat deeper, due to some increase in leaching
as a result of the low water-holding capacities of the various soil layers.
The depth of this very saline layer corresponds to a large extent with the
depth of maximum water penetration measured during recent years (Gerson
and Amit, 1982). The water penetration after a heavy rainfall of 30-35 mm
reached about 25 cm in the mature Reg soils and about 40 cm in the young
Reg soils and coarse desert Alluvium which is not affected by floods and
where the beginning of the Reg soil formation may be recognized (as in
profile 2). The deeper water penetration of the young Reg soils is related to
the low water-holding capacity (only about 10% at field capacity according
to measurement near Zofar (D. Russo, personal communication 1980). This
depth corresponds with the beginning of the most saline layers in the various
profiles. After an exceptionally heavy rainstorm such as that which occurred
during 19/2-21/2 1975, when the rainfall in the southern Negev reached
60-80 mm, the water penetration was somewhat deeper but even on this
occasion it did not exceed 50-60 cm in the mature Reg soils.
In the young Reg soils this water penetration is somewhat deeper and
youno~st
195
EC VALUES (mmho/cm)
100
50
150
~o
e 0.5
:c
I-
<>-
w
Q
'"en
_ _ _ Prof. 1 COPRS£ DESERT AlluVIUM
(Recent surface)
______ Prof. 1 VERY YOUNC ~EGOSOLlC REG
(Li ~·an surface)
•••••••••••• Prof. 3 REGOSOLIC REG
(mid-Pleistocene surface~
_ . _ . - Prof. 4 DEEP REGOSOLI C REG
1.0
(Neogene surface)
I.S,.L..------------------------------i
Fig. 6. Conductivity values of the profiles in the vicinity of Hazeva and central Sinai
(profiles 1-4).
EC VALUES (mmho/cm)
-·----1
J -.....
i
I0
ISO
2
4::~~ ._. -"'1,
".\----- ____ .-1'
/'~r/·
,I .
.
·1
'( ,;
0.5
),
• I
.ti
I,r
e
,,,!..
II'
:c
1 .~
I-
<>w
'"
Q
~!i
~1.0
~
"!
..
I
,,I i
" !
" ,, .
,
.
1.5
- - - Prof. 5
COARSE DESERT ALLUVIL't1
- - - - .. Prof. 6
YOUNr. REGOSOLIC REG
........ _. Prof. 7 MATURE REGOSOL!C REG
Fig. 7. Conductivity values of the soils near Bir-eth Thamada (profiles 5-7).
196
reached 75 cm. This was followed by the deeper leaching of the salts. The
depth of water penetration during this storm may correspond to the deeper
part of the most saline layer in the Reg soils.
The deeper soil layers of profiles 3, 4, 6 and 7 are characterized by very
high gypsum contents (Figs. 8 and 9), whereas the salinity values decrease
slowly with depth. Most of this gypsum cannot be related to the present rainfall regime as this layer is found beneath the main sa horizon. The occurrence
of this gypsum may be related to a somewhat more rainy period in the past,
although some of it may be formed even nowadays after the heaviest rainstorms. This deep gypsum layer is absent in profile 2. Inprofile 6 it is not
significant (the main gypsum layer of this profile is found at a depth of 2234 cm) due to the young age. The deep gypsic layers of the older soils, especially that of profile 4, apparently developed during a more rainy period in the
past. Below 1 m the gypsum contents in profiles 3, 4 and 7 decrease again
slowly, whereas the salinity values rise again to somewhat higher degrees.
This may be the beginning of a saline horizon related to the old gypsum pan,
but most of the salt related to that gypsum pan should be found only in still
deeper layers, as the total gypsum contents of the various pans are very high,
whereas the other salt contents are relatively low in the layers that have been
analyzed. No increase in the salinity of the deepest layers of profile 6 was
detected, an indication of the younger features of this soil.
GYPSUM (%)
D.5
2
5
10
20
50
50
~
::z:
....
CL
....
C
.....
Q
(I)
100
_ _ Prof. I
COARSE OESERT ALLUVIUM
(Recent surface)
150
_____ Fref. 2
V£R" YOUNG REGOSOLIC REG
(l ;san surface)
........... Prof.
REGOSOLIC REr.
(mid-Pleistocene surface)
_._._.- Pcof. 4 DEEP REGOSOllC REG
(r.eo~enE surface)
Fig. 8. Gypsum contents of the profiles in the vicinity of Hazeva and central Sinai (profiles
1-4).
197
GYPSUM ,,,)
5
III
i··· .. ·.. ·.....
2
20
10
5
50
_..... _..... -j------._-,r- --.- -- _____ _
... ... ...
•.•. j.
:.~
;·i. . . . " , ........,
·············.1•...•. _.•.•.•.•.
I
••
.,
I
I
I
0.5
')i~
",
~.,
..' I'
-e
. \,
'i
II
%
....t
Q
:I
.....
o
•
"'lD
i
.
I
/:
,.
" I,
I
i!
.'1
"
I
.........
"
."~
.~ ..... I
:,'
I
~
I
I
.......;
L .....·
' ..., ..... ·r
/~I
I
,,!
:
/'
~
,/
~
1.5
I
I
I
~~~
I
~~
~
,,,
I
I
- - - Prof. 5 COARSE OESERT ALLUVIUM
,/
••••• - . Prof. 6 YOUNG REGOSf.L1C REG
-'-'-'-' - Prof. 7 MATURE REGOSOLIC REG
Fig. 9. Gypsum contents of the soils near Bir-eth Thamada (profiles 5-7).
Age estimate of the various Reg soils from salt accumulation
The salinization of the Reg soils may be related to atmospheric automorphic salinization (Yaalon, 1963). The various soils checked show evident increases in salinization, passing from the soils on the youngest, lowest surfaces
to the soils on the oldest, highest surfaces_ Calculations were made for the
seven profiles to test the possibility of estimating the ages of these soils from
salt and gypsum contents.
The following calculations were based on several assumptions, viz., that
the annual fall-out of salts was more or less similar to the prevailing fall-out
at Sde Boqer (Yaalon, 1964b), i.e., that the deposition of sodium, on which
the calculation of the most soluble salts was based, reached 2 kg/ha and that
of S04 anions (calculated for gypsum) reached 10 kg/ha. (At Sde Boqer the
value was 9 kg/ha but the amount at Mizpe Ramon, which is nearer the desert,
was much higher, so that a value of 10 kg seemed reasonable.)
The actual data may deviate considerably from the calculated figures for
the following reasons:
(1) The rainfall figure of 50 mm may be too high, as the average rainfall
in the desert region (Arava Valley and central Sinai) is somewhat lower. At
Nakhl, the nearest point to Bir-eth Thamada, the average rainfall reached 27
mm (Ganor et al., 1973). At Kuntilla and Thamad, the stations in the vicinity
198
of profile 4, the figures reached 32 and 37 mm, respectively, whereas the corresponding figure for En Yahav, near Hazeva, was 42 mm (Israel Meteorological Service, 1967). Moreover, these figures include the salts in runoff water,
which is very significant in the desert. The real average airborne salinization rate
may thus reach only 50% or even less of the salt content figures, so that the calculated time scale might be at least doubled.
(2) The calculation was based on the present rainfall figures. As already
mentioned, rainfall may have been somewhat higher during some periods in
the past (Bull and Schick, 1979; Gat and Magaritz, 1980). The salt accretion
figures should thus be somewhat higher; they may have reached or even exceeded these for the Sde Boqer area.
(3) The rainfall salinity figures were based on those for the Negev mountains. The figures for the Arava Valley, and especially those for central Sinai,
might be somewhat different inasmuch as the rainfall regime in these regions
includes some spring and fall storms connected with depressions in the Dead
Sea region (Ganor et al., 1973).
(4) The calculations were based only on the salt and gypsum contents in
the soil profile and did not include the amounts of these compounds in
deeper layers. This might be especially important for the profiles where the
salt and gypsum contents are quite high in the deepest soil layers, such as
profiles 3, 4 and 7. The real salt accumulation figures for these profiles may
thus be much greater. The same may hold true for the gypsum values of
profile 4 and also for profile 7, as some gypsum pans were found even in
the deepest soil layers.
(5) The calculation of S04 accumulation was based only on the gypsum
contents, but some other sulphate salts are also present. The calculation based
on gypsum might thus be somewhat too low, which would affect especially
the calculations from. the younger profiles where the gypsum content is low.
The age-estimates based on the salt and gypsum contents of the various
profiles are given in Table III.
TABLE III
Estimation of age of the various profiles*
Profile no. and surface
Estimation based on
salinity contents
(years)
Estimation based on
gypsum contents
(years)
2. Lisan surface
3. Mid-Pleistocene surface
4. Early Pleistocene-Neogene surface
5. Holocene surface
6. Mid-Pleistocene surface
7. Mid to early Pleistocene surface
9500
50700
61200
2900
20100
19700
3500
127000
190000
1500
57100
65500
*Calculated ages are rounded to the nearest 100 years.
199
The age figures calculated according to the salinity contents differ from
those calculated according to the gypsum contents. In profiles 2 and 5 the
values for sulphates would have been much higher if the total contents of
sUlphates had been calculated and these figures would then approach those
of the salt-age calculation figures.
For the other profiles, the age-estimates based on salt content are much
lower than those based on gypsum, especially for profile 4 and to a somewhat
lesser degree also for profiles 3 and 7. The gypsum values therefore seem better for these cases, as the salt-age figures may be related mainly to the recent
more arid cycle. But even the gypsum figures generally indicate too low ages,
suggesting that some gypsum had been leached into deeper layers or that the
supply was lower in the past. Horowitz (1979) claims that several changes in
climate during the Pleistocene occurred in all of Israel, including the deserts;
therefore, sometime in the past, the area may have received somewhat higher
rainfall and, as a result, soluble salts were leached to great depths. It is possible
that this somewhat more rainy period corresponded more or less with the beginning of the last glaciation, i.e., about 90000 B.P. It is not feasible to estimate
the rainfall during that more rainy period in the past. The annual amount could
not have exceeded 200 mm, or the gypsum would have been leached, as this is
the present limit for gypsum concentrations in medium-textured soils in the
northern Negev (Dan and Yaalon, 1980). Moreover, this limit for stony and
coarse textured soils such as the Regs is much lower because of the low water·
holding capacity of such soils. Thus, the average annual rainfall figures for the
rainy period in the Arava and central Sinai probably could not have exceeded
100 mm. The total absence of loess also confirms this low figure, as loess
deposits would have been found in the desert if it had received more than 100
or 150 mm rainfall (Dan et al., 1981).
The differences between the salt and gypsum profile figures of the older
soils may also help us to evaluate their relative age and their salinization
history. Profile 6 seems to be the youngest of these profiles, as only one
definite salt and gypsum horizon was found and the values of both compounds dropped to low values at depths greater than 34 cm. It thus seems
that this profile was affected only by the present arid climatic cycle; otherwise the gypsum contents of the deeper soil layers would be much more signigicant. The gypsum horizons in profiles 3 and 7 reach deeper layers, but
even in these profiles the gypsum values in the deepest layers fall to quite
low figures. These profiles probably enjoyed a somewhat more rainy period
in the past, but very little gypsum penetrated deeper, and their age estimates
would thus correspond, approximately, to the figures calculated from the
gypsum content. In profile 4, on the other hand, high gypsum values were
still found in the deepest soil layer, and this profile probably enjoyed, during
the Middle Pleistocene, another moist period when the rainfall leached some
of the gypsum to the still deeper layers.
Classification and correlation
Differences in the ages of the soils are well expressed by the soil charac-
200
teristics and this is also reflected in classification of the soils. The youngest
soils (profiles 1 and 5) do not yet show any horizon development and would
thus be classified as Coarse desert Alluvium according to the Israeli Classification (Committee on Soil Classification in Israel, 1979) or as Typic Torriorthents according to the American classification system (Soil Survey Staff, 1975).
Profile 2 already has minimal profile development and should thus be classified as a very young Reg, but the weathering zone is very shallow, so that
even a shallow ploughing would destroy and eliminate these profile characteristics. This profile would thus still be classified as a Coarse desert Alluvial
soil or a Typic Torriorthent.
Profiles 3, 4, 6 and 7 already have either well or faintly expressed cambic*!
and gypsic horizons as well as all other properties which characterize the Reg
soils. These soils would thus be classified as Typical Regs according to the
Israeli classification and as Gypsiorthids or even partly as Petrogypsic Gypsiorthids according to the American classification system. It seems that some
of the younger Reg soils, in which the gypsum content is not very high, and
where the petrogypsic horizon has not yet developed, would have been classified as Typic or Cambic Gypsiorthids in the American system.
ACKNOWLEDGEMENT
The authors wish to thank Dr. Hanna Koyumdjisky for her great help and
her useful remarks.
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201
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