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Do red beds indicate paleoclimatic conditions?:
A Permian case study
Nathan D. Sheldon*
Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom
Received 27 September 2004; received in revised form 25 February 2005; accepted 16 June 2005
Abstract
Terrestrial red beds have long been interpreted as desert deposits by comparison with modern red deserts. More recently red
beds have been interpreted as evidence of seasonally dry conditions and a Permo–Triassic Pangean monsoon. Red beds of Cala
Viola, Sardinia are identified as paleosols and used to reconstruct Late Permian paleoclimatic conditions. Reconstruction of
paleoenvironmental conditions based on the paleosols of the Cala Viola indicates warm, humid conditions with no evidence of
dry conditions, as in a desert, or of extreme seasonality as in a monsoon. Instead, it is suggested that the red color of the
paleosols is a result of former good drainage, and that red color in general does not indicate specific paleoclimatic conditions.
D 2005 Elsevier B.V. All rights reserved.
Keywords: Permian; Sardinia; Paleosols; Paleoclimate; Monsoon
1. Introduction
A long held dogma is that widespread Triassic
terrestrial red beds indicate a global transition to warm-
er and drier conditions than those that characterized the
Permian (Parrish, 1995). This new climatic system has
been termed the Pangean mega-monsoon (Kutzbachand Gallimore, 1989). The question to be addressed
herein is whether red color alone is sufficient evidence
upon which to base paleoclimatic interpretations.
Early research on modern red deserts supported the
interpretation that ancient red beds formed in hot, dry
climates (Walker, 1976). However, modern red deserts
of Arizona and Australia are red because of sediments
recycled from paleosols of Triassic and Miocene age,
respectively, and most deserts of North and South
America, Asia, and the Middle East are grey like
their weathering source rocks. Further, many red
soils in semi-arid areas such as New Mexico derivedtheir red color from well-drained, warm conditions
during Pleistocene pluvials, so the red color is relict
and related to earlier paleoenvironmental conditions.
More recently, Parrish (1998, p. 192) stated that ter-
restrial red beds, b. . .appear to be indicative of cli-
mates that are warm and dry or seasonal with respect
to rainfall. Q A model put forth by Dubiel and Smoot
(1994) suggests that continental red bed formation is
0031-0182/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.palaeo.2005.06.009
* Tel.: +44 1784 443615.
E-mail address: [email protected].
Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305–319
www.elsevier.com/locate/palaeo
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favored by warm climates with alternating wet-and-
dry seasons (monsoons) and open, desert to savanna
vegetation. However, it is not an exact analog because
a true savanna requires grasslands, which did not evolve until the Cenozoic (Retallack, 2001a; Terry,
2001). Monsoonal tropical Pakistan and India include
both grey and red soils and paleosols (Retallack,
1991a). Wynn (2000) and Wynn and Retallack
(2001) describe reconstructed savanna ecosystems
from Cenozoic paleosols in Africa that are not signi-
ficantly reddened. Furthermore, numerous examples
have been published of diagenetic reddening of non-
desert paleosols by dehydration of iron oxyhydroxides
(Retallack, 1991a, 1997, 2001b; see also the review of
older literature in Blodgett et al., 1993).Taken together, these various factors suggest that
the origin of red color may not be well-understood or
well-explained by existing models. Work presented
here on Late Permian red beds in Sardinia offers an
alternative explanation to pronounced aridity or sea-
sonality. It is suggested that the red color is indicative
of well-drained conditions and that it provides no
unequivocal information on the paleoclimatic condi-
tions at the time of paleosol formation. Instead, paleo-climatic conditions are reconstructed on the basis of
other proxies, such as the degree of chemical weath-
ering, nature and extent of pedogenic carbonate and
salts, and patterns of root traces and trace fossils.
2. Geologic context
Basin-and-Range topography was a result of the
Carboniferous–Permian Hercynian orogeny from eastern
Europe to the southern coast of the United States(Cortesogno et al., 1998). Collision of South Europe
with North America and Afr ica during the Late De-
vonian and Carboniferous (Condie, 1989) was fol-
lowed, through Triassic time, by local rifting and
formation of continental basins in Spain, Southern
Fig. 1. Map showing the location of field sites and stratigraphic column for the Lago di Baratz section, Verrucano Sardo Formation. LB01-15 are
sample numbers, and Munsell colour of the sample is to the right of the sample number. The exact transition between the lesser developed
Mosca Pesca and Lago di Baratz paleosols and the overlying Mácchia paleosols is unknown and may lie in the covered interval (shown with an
X) rather than at the first logged Mácchia Rossa paleosol.
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France, Italy, Corsica, and Sardinia (Cassinis and
Ronchi, 1997). These basins were filled with clastic
red beds derived from the orogenic belt.
In Sardinia, those sediments are part of the Verru-cano Sardo Formation exposed on the Cala Viola
(bviolet bay Q ) (Fig. 1), and are divided it into four
informal units (Gasperi and Gelmini, 1979). The red
beds described in this paper are from bUnit 2, Q a 150
m package of sediments composed of sandy conglom-
erates, grey sandstones, and red sandstones and mud-
stones. The Cala Viola Nord section is capped by a
thick, quartz cobble conglomerate that is also exposed
near the base of the Cala Viola Sud section (Fig. 1).
The rocks exhibit fluvial paleochannels, tetrapod foot-
prints, and fossil plants indicating subaerial depositionon alluvial fans and floodplains. Gasperi and Gelmini
(1979) examined the limited available fossil assem-
blages and found Autunian (Early Permian) non-ma-
rine strata near the base of the sequence and Triassic
red claystones and sandstones near the top [Units 3
and 4], overlain by Middle Triassic (Anisian–Early
Ladinian) limestone (Cassinis and Ronchi, 1997; Cas-
sinis et al., 1992). The red beds described here are
located near the top of the sequence (top of Unit 2),
and are thus Late Permian in age (Cassinis et al.,
1992).
The Lago di Baratz area (Fig. 1) is well vegetated
and exposure is generally poor. Three of the four
pedotypes are exposed in this section (Fig. 1), includ-
ing the Lago di Baratz and Mosca Pesca pedotypes,
which are not preserved in either of the Cala Viola
sections. In contrast, the Cala Viola sections, with
localized gentle folding, are well-exposed in sea cliffs
and rock platforms, and are continuous and conform-
able with significant lateral variability difficult to
capture adequately in single stratigraphic sections
(Figs. 2 and 3). The Lago di Baratz section lies
stratigraphically below the Cala Viola sections by anunknown thickness of mudstones and sandstones in
Unit 2 of Gasperi and Gelmini (1979). However,
given that only the middle and upper portions of
Unit 2 are red and the lower portion is primarily
grey, it is possible that the red Mácchia paleosols of
the Lago di Baratz section (Fig. 1) represent the first
red beds. If this is the case, given the 75–85 m
exposed in the Cala Viola sections (Figs. 2 and 3)
and a total thickness of 150 m for Unit 2 (Gasperi and
Gelmini, 1979), there can be no more than a few tens
Fig. 2. Stratigraphic column for the Cala Viola Nord section,
Verrucano Sardo Formation. Symbols and conventions are as in
Fig. 1. Asterisks next to sample numbers indicate samples that were
weakly reactive to dilute acid. The thicknesses of the conglomerate
that caps the Cala Viola Nord and Sud sections are variable, so the
average thickness is portrayed. Where multiple lithologies are
shown, there is significant variability along strike and additional
symbols apply to the right column, which represents the dominant
lithology.
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of meters between the top of the Lago di Baratz
section and the bottom of the Cala Viola Nord section.
3. Methods
Paleosols were recognized in the field on the basis
of ped morphology, horizonation, root traces, and
grain size changes (Retallack, 1997). Munsell color
was recorded as well as the qualitative degree of
calcareousness on t he basis of reaction with dilute
hydrochloric acid (Retallack, 1997). Samples werecollected for petrography and geochemical analysis
from three sites north of Alghero, near Lago di Barat z
and at two localities on the Cala Viola (Fig. 1).
Geochemical data were obtained from a commercial
laboratory (Intertek of Vancouver, B.C.) using XRF,
ICP-MS, and titration (FeO) and are compiled in
Table 1. Paleosols were classified into pedotypes
(Retallack, 1997; Retallack, 2001b) on the basis of
physical and chemical characteristics (Sheldon and
Retallack, 2001; Sheldon et al., 2002), and analyzed
using the factor function approach (Jenny, 1941).Bulk density (q) was measured by the clod method
using paraffin; analysis of 10 replicates of a single
sample gave an uncertainty of 0.09 g cm3.
4. Evidence of pedogenesis
Paleosols in the Cala Viola sections fine up-profile
and are notably finer grained than the succession as a
whole (Figs. 2 and 3). This difference shows up in the
weathering profile of the sections as well (Fig. 4A)
and in contrast to the fluvially-derived sandstones
(Fig. 4B). Many of the paleosols also preserve drab-
haloed root traces (Fig. 4C,F) and rarely, vertical
burrows (Fig. 4C,D). Burrows range up to one cm
in diameter and show some internal structure consis-
tent with backfilling by an arthropod. Non-calcareous
rhizoliths are well-preserved in some of the paleosols,
both in hand specimen and thin section (Fig. 4H).
Both root traces and burrows penetrate deeply into
paleosol profiles (Fig. 4C), indicating that the paleo-
water table was substantially below the surface. Point
counts of thin sections (e.g., Fig. 4E,H) are consistent with the field observation that paleosols are more fine-
grained than interfluve sandstones, siltstones, and
mudstones. Some of the Cala Viola paleosols have
an observed clay bulge (Fig. 5) and illuviation argil-
lans observable in thin section consistent with subsur-
face accumulation of clay in a Bt horizon. A and B
horizons of paleosols have 80–97% clay and phyllo-
silicate minerals and 3–20% quartz and lithics (includ-
ing feldspars) with an average of less than 10%,
whereas C horizons and other fluvial sediments all
Fig. 3. Stratigraphic column for the Cala Viola Sud section, Verru-
cano Sardo Formation. Symbols and conventions are as in Fig. 1.See Fig. 2 caption for additional information.
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Table 1
Geochemical data
Sample Level
(m)
React a Horizon SiO2 TiO2 Al2O3 Fe b FeO Fe2O3 MnO MgO CaO Na2O K 2O P2O5 LOI Total
LB02 3.6 N 77.98 0.37 12.64 1.80 0.45 1.30 0.02 0.27 0.07 n/a 1.85 0.07 4.03 99.1
LB03 4.4 N A/Bwc 78.63 0.30 9.62 4.81 0.39 4 .37 0.03 0.21 0.08 n/a 0.97 0.12 4.16 99.3
LB04A 5.9 N C 66.80 0.70 14.89 7.30 0.51 6.73 0.05 0.60 0.16 0.10 2.75 0.15 5.79 99.8
LB04B 6.0 N C 70.08 0.81 17.22 1.68 0.45 1.19 0.01 0.74 0.09 0.19 3.40 0.05 5.31 100.0
LB04C 6.2 N A/Bw 69.27 0.84 17.08 1.73 0.51 1.16 0.02 0.66 0.06 0.20 3.56 0 .05 5.08 99.1
LB04D 6.4 N A 67.22 0.70 15.35 6.52 0.58 5.88 0.05 0.59 0.09 0.08 2.88 0.11 5.66 99.8
LB11 13.0 N C 75.11 0.52 14.21 2.83 0.45 2.33 0.03 0.62 0.11 0.03 2.48 0.07 4.29 100.8
LB12 13.2 N C 66.15 0.72 16.84 5.58 0.71 4.79 0.02 1.14 0.12 0.14 3.95 0.08 4.99 100.4
LB13 13.5 N C 61.17 0.80 18.76 6.54 0.71 5.75 0.02 1.40 0.08 0.17 4.82 0.06 5.27 99.8
LB14 13.7 N Bw 62.34 0.79 18.84 5.15 0.90 4.15 0.02 1.30 0.10 0.21 4.69 0.06 5.93 100.3
LB15 13.9 N A 61.20 0.78 18.63 7.02 0.64 6.31 0.02 1.32 0.08 0.15 4.70 0.08 5.30 99.9
CV03 1.7 N Bw 58.00 0.92 19.18 6.61 0.84 5.68 0.05 1.81 0.90 0.16 5.22 0.06 6.67 100.4
CV06 4.2 N 56.05 0.84 16.17 6.06 1.61 4.27 0.13 2.60 3.50 0.23 4.05 0.07 9.78 101.1
CV07 5.5 N C 48.79 0.72 16.40 6.19 0.71 5.40 0.46 4.30 5.26 0.22 4.41 0.09 12.5 100.0
CV08 5.8 N Bt 54.82 0.87 19.81 6.40 1.03 5.26 0.07 2.21 1.50 0.17 5.47 0.12 7.92 100.4
CV09 6.1 N Bt 56.93 0.91 20.65 6.49 0.90 5.49 0.02 1.67 0.28 0.15 5.72 0.12 6.27 100.1
CV10 6.5 N A 57.71 0.91 20.21 6.98 0.77 6.12 0.02 1.57 0.20 0.18 5.27 0.08 6.12 100.0
CV13 10.1 N 56.05 0.91 19.22 6.32 0.90 5.32 0.07 2.00 1.31 0.16 5.30 0.08 7.39 99.7
CV16 12.4 N C 55.56 0.78 14.59 6.55 1.74 4.62 0.18 3.03 4.20 0.32 3.79 0.04 10.7 101.4
CV19 14.1 Y C 56.24 0.86 16.04 3.47 1.87 1.40 0.17 3.12 4.47 0.18 3.87 0.09 11.1 101.5
CV22 17.2 Y Bt 30.48 0.47 9.25 3.30 1.03 1.51 0.91 10.6 15.5 0.29 2.26 0.06 26.7 100.8
CV24 19.15 N C 56.12 0.59 13.94 4.64 1.42 3.07 0.18 3.27 5.08 0.26 3.58 0.05 11.4 100.5
CV25 19.85 N Bt 51.90 0.63 11.69 4.83 0.51 4.26 0.34 4.77 7.67 0.19 2.89 0.07 14.2 99.7
CV26 20.65 Y A 14.89 0.25 4.99 2.98 0.26 2.69 0.91 15.1 22.6 0.22 1.10 0.07 35.4 98.8
CV27 22.05 Y Bt 56.94 0.89 19.69 7.98 0.77 7.12 0.02 1.44 0.29 0.09 5.79 0.14 5.82 99.9
CV28 23.2 N C 53.35 0.83 15.45 5.58 0.77 4.72 0.06 1.50 1.90 0.22 4.24 0.09 6.61 90.6
CV29 24.2 N Bt 59.56 0.89 19.87 6.59 0.64 5.88 0.03 1.24 0.19 0.17 4.95 0.12 5.43 99.7CV30 24.9 N Bt 57.89 0.93 20.01 8.35 0.58 7.71 0.03 1.20 0.14 0.12 4.77 0.11 5.75 99.9
CV31 26.15 N 55.13 0.61 11.67 4.29 0.51 3.72 0.15 1.18 6.57 0.56 2.41 0.05 11.5 94.6
CV45 46.5 N C 58.99 0.40 6.22 1.26 0.32 0.90 0.12 6.17 9.31 0.25 1.57 0.03 14.5 99.1
CV46 48.0 N BC 58.65 0.71 12.04 3.43 0.45 2.93 0.09 4.28 5.56 0.59 2.85 0.04 9.89 98.6
CV47 49.25 N Bw 83.50 0.26 8.57 1.23 0.45 0.73 0.01 0.28 0.22 0.05 1.57 0.03 2.75 99.0
Sample Rho
(g cm3)
CIA K Clayeynessd (P
bases/Al)d Salin.d Gleyd MAP MAT Bae Sr Y Nb Zr Rb
LB02 2.52 0.095 0.22 0.16 0.77 132 66 25 28 164 112
LB03 2.39 98.51 0.07 0.18 0.11 0.198 1540 15.3 76 36 18 18 141 72
LB04A 2.58 0.13 0.33 0.21 0.17 351 92 31 21 257 137
LB04B 2.49 0.15 0.35 0.23 0.84 362 127 42 28 312 194
LB04C 2.50 97.49 0.15 0.35 0.24 0.98 1509 12.8 377 116 37 22 281 180LB04D 2.55 98.11 0.13 0.32 0.21 0.22 1528 13.4 293 95 29 22 260 151
LB11 2.59 0.11 0.32 0.19 0.43 208 61 23 22 229 159
LB12 2.59 0.15 0.45 0.27 0.33 358 107 36 28 280 240
LB13 2.64 0.18 0.49 0.29 0.27 423 121 34 21 215 292
LB14 2.53 97.28 0.18 0.47 0.29 0.48 1503 12.0 405 123 33 28 229 293
LB15 2.54 97.94 0.18 0.47 0.29 0.23 1522 12.0 398 128 38 23 225 276
CV03 2.71 90.99 0.195 0.63 0.31 0.33 1328 11.6 622 117 37 23 171 266
CV06 2.70 0.17 1.095 0.29 0.84 1636 134 34 21 284 195
CV07 2.71 0.20 1.56 0.31 0.29 544 122 34 16 144 210
CV08 2.81 86.82 0.21 0.73 0.31 0.44 1223 11.5 998 105 30 22 114 262
(continued on next page)
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have 15–35% quartz and lithics, with an average of
about 20%. Many of the fluvial sediments, and two of
the paleosols, have non-calcareous sandy concretionsranging in size from mm-scale (Fig. 4E) to decimeter
scale. Typically these are grey-green, fine- to medium-
grained sand in otherwise red sediments. Grey-green
color in iron-bearing paleosols is typically associated
with unoxidized iron. These apparent micro-reducing
conditions may be attributable to the former presence
of decaying organic matter, and may have been
formed in a fashion similar to the drab-haloed root
traces.
Bulk rock geochemical properties of fluvial rocks
may also be used to identify paleosols and to separate paleosol orders (Sheldon et al., 2002). Net gains and
losses of different elements may be calculated by
examining the mobility of the element of interest
relative to some assumed immobile element (Chad-
wick et al., 1990; e.g., Driese et al., 2000). Elements
that are typically considered as immobile during
weathering include Ti, Zr, Nb, Hf, and under some pH conditions, Al. Ti, Zr, and Nb were considered and
Ti was selected both because it was immobile relative
to Zr and Nb and because it is the most abundant of
the three elements. The open system mass-transport
function for element j in the weathered sample (w)
is defined as follows (e.g., Chadwick et al., 1990):
s j;w ¼ qwC j;w
= q pC j; p
ei;w þ 1
1 ð1Þ
where qw is the density of the weathered material,
C j,w is the chemical concentration (weight percentage)of element j in the weathered material, q p is the
density of the parent material, and C j,p is the chemical
concentration (weight percentage) of element j in the
parent material. If s j,w=0 (i.e., element w was immo-
Sample Rho
(g cm3)
CIA K Clayeynessd (P
bases/Al)d Salin.d Gleyd MAP MAT Bae Sr Y Nb Zr Rb
CV09 2.77 96.47 0.21 0.54 0.31 0.36 1479 11.5 449 98 33 24 120 280CV10 2.74 96.84 0.21 0.51 0.30 0.28 1490 11.8 418 94 30 21 153 270
CV13 2.74 0.20 0.70 0.31 0.38 1081 125 27 25 147 260
CV16 2.64 0.15 1.37 0.32 0.84 951 92 36 19 237 184
CV19 2.65 0.17 1.28 0.28 2.97 959 113 42 19 301 196
CV22 2.76 0.18 6.26 0.32 1.52 537 87 43 10 93 94
CV24 2.67 0.15 1.56 0.31 1.03 2439 136 33 16 195 163
CV25 2.58 0.13 2.52 0.29 0.27 2434 142 41 12 306 124
CV26 2.82 0.20 16.2 0.31 0.22 9654 272 29 nd 31 40
CV27 2.74 96.68 0.21 0.54 0.33 0.24 1485 11.3 507 158 33 24 125 270
CV28 2.54 0.18 0.79 0.32 0.36 51,452 1017 22 nd 151 178
CV29 2.70 96.95 0.20 0.46 0.28 0.24 1493 12.0 3292 262 32 22 159 244
CV30 2.72 97.79 0.20 0.43 0.27 0.17 1518 12.3 367 179 47 21 173 241
CV31 2.60 0.13 1.58 0.30 0.31 34,767 688 30 9 269 95CV45 2.69 0.06 5.57 0.34 0.79 275 73 34 20 202 79
CV46 2.75 0.12 2.08 0.34 0.34 303 107 32 22 390 138
CV47 2.60 94.67 0.07 0.37 0.21 1.37 1428 13.4 144 78 17 23 133 102
a Reactive with dilute HCl. b Total iron as Fe2O3.c Refers to samples at the boundary between two horizons.d Molar ratios: clayeyness= (Al2O3 /SiO2);
P bases / Al = (CaO + MgO + Na2O + K 2O)/Al2O3; salinization (Na2O + K 2O)/Al2O3; gleiza-
tion=(FeO/Fe2O3).e All trace element compositions.
Table 1 (continued )
Fig. 4. Field and petrographic photos. A) Outcrop photo of the Cala Viola Nord section; paleosols sit on top of the coarser, horizontal benches in
the section (arrow). B) Outcrop photo showing the complex fluvial character of Verrucano Sardo Formation. C) Profile of a Cala Viola paleosol;
the light colored vertical streaks are rhizoliths and drab-haloed root traces (arrows). D) Close-up of vertically oriented burrows in a paleosol A
horizon (arrow). E) mm-scale quartz concretion (sample CV-20). F) Root traces (arrow) deep in the C horizon of a paleosol, penetrating nearly
to into the A horizon of the underlying paleosol. G) Laterally discontinuous ground water gleying (arrow) features where the water table was
ephemerally closer to the surface. H) Thin section of a root trace (sample CV-12).
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bile), then ei,w can be solved for separately allowing
us to bypass volume (as in the classical definition of
strain) as follows (e.g., Chadwick et al., 1990):
ei;w ¼ q pC j; p
= qwC j;w
1 ð2Þ
where ei,w is the strain on immobile element i in the
weathered sample. The parent materials for the profiles
were overbank mudstones and sandstones as appropri-
ate, with separate geochemical analyses for each of the
paleosol profiles (Table 1; lowermost C horizon anal-
yses). Fig. 6 shows the losses or gains of Ca and Sr
(which occupy the same sites in most minerals) in the
type Mácchia and Cala Viola paleosols assuming Ti
was immobile during weathering (calculated following
Chadwick et al. (1990)). Although both pedotypes have
lost much of their Ca relative to their parent material,
the Cala Viola paleosol has clearly been more weath-
Fig. 5. Chemical degree of weathering. A) Ca and Sr loss in the type Mácchia and Cala Viola paleosols assuming Ti is immobile. A tau value of
1 represents 100% loss of Ca relative to the parent material, and a tau value of 0 represents the parent material. Both paleosols lost Ca, withthe Cala Viola type profile showing greater Ca loss, consistent with a greater degree of chemical weathering. Other elements such as Sr show
more complicated changes, but are still consistent with a greater degree of chemical weat hering in the ty pe Cala Viola profile. B) Additional
geochemistry (CIA K (Maynard, 1992) and clayeyness (molar ratio of alumina to silica; Retallack, 1997)). of the type Cala Viola profile Thesignificant offset between values low in the profile and high in profile is evidence of intense chemical weathering. The clayeyness index shows a
b bulge Q consistent with the field identification of a Bt horizon.
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ered, a finding consist ent with the field classification of
the paleosols (Table 2). Paleosols generally exhibit the
highest degree of chemical weathering within their Aand B horizons, with a decrease in weathering down
profile. Fig. 5B shows the chemical index of alteration
without potash (Maynard, 1992) for the type Cala Viola
paleosol. This pattern is consistent with pedogenesis
rather than fluvial sedimentation where one would
predict a more erratic variation from bed to bed, but
where most values would cluster around a btypical Q
value for the whole sedimentary succession.
4.1. Pedotypes
Four pedotypes (sensu Retallack, 1994) were
identified and given names in Italian from their
field localities or reconstructed similarity to a given
environment.
4.1.1. Cala Viola ( bviolet bay Q )
The type Cala Viola paleosol crops out in the
northern Cala Viola section. Cala Viola paleosols are
comparable to modern Alfisols (Soil Survey Staff,
1998) in the USDA soil classification scheme (Table
2). They are moderately developed (see Retallack (1988) for definitions of the degree of development),
with no relict bedding, blocky peds, and subsurface Bt
or Bw horizons. Cala Viola profiles are typically A–
Bt–C, and represent a fairly stable landscape (i.e.,
infrequently flooded; Table 3).
4.1.2. Lago di Baratz ( b Baratz’s lake Q )
The type Lago di Baratz paleosol crops out in the
Lago di Baratz section. Lago di Baratz paleosols are
comparable to modern Entisols (Soil Survey Staff,
1998) in the USDA soil classification scheme (Table
2). They are very weakly developed, with some relict
bedding and no diagnostic subsurface horizons. Lago
di Baratz profiles are A–C and represent a frequently
disturbed landscape (i.e., flooded; Table 3).
4.1.3. Mácchia ( bunderbrush Q )
The type Mácchia paleosol crops out in the Lago di
Baratz section, and Mácchia paleosols are found in
both field areas. Mácchia paleosols are comparable to
modern Inceptisols (Soil Survey Staff, 1998) in the
USDA soil classification scheme (Table 2). They are
weakly developed with little relict bedding or pedstructure. Mácchia profiles are A–(Bw)–C and repre-
sent a fairly stable landscape (Table 3).
4.1.4. Mosca Pesca ( b fly fishing Q )
The type Mosca Pesca paleosol outcrops in the
Lago di Baratz section. Mosca Pesca paleosols are
comparable to modern Entisols (Soil Survey Staff,
1998) in the USDA soil classification scheme (Table
2). They are very weakly developed, preserve relict
bedding, lack ped structure, and lack diagnostic sub-
Fig. 6. Gleization for the type profiles of the Cala Viola and Mácchia pedotypes. Gleization is the molar ratio of ferrous (Fe2+) to ferric
(Fe3+) iron.
Table 2
Cala Viola pedotypes
Pedotype Diagnosis FAO USDA
Cala Viola Thick and red with clayey
subsurface (Bt) on alluvium
Luvisol Alfisol
Lago di
Baratz
Grey-green silty soil with
some relict bedding and no
diagnostic subsurface horizons
Fluvisol Entisol
Mácchia Variable thickness red
sometimes with scattered
drab haloed root traces and
no subsurface Bt or Bk
Cambisol Inceptisol
Mosca
Pesca
Sandy, relict bedding,
without horizonation
Fluvisol Entisol
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surface horizons. Mosca Pesca profiles are AC–C and
represent a frequently disturbed landscape (Table 3).
5. Diagenesis
Paleosols typically undergo a number of diagenetic
changes including loss of organic matter, burial red-
dening due to dehydration of oxyhydroxides (e.g.,
conversion of goethite [Fe(OH)3] to hematite
[Fe2O3]), and compaction due to burial beneath an
overburden (Retallack, 1991b). Paleosols of the Cala
Viola preserve essentially no organic matter (b1%
by volume in thin section point counts). Studies of
Quaternary (Stevenson, 1969) and older (Retallack,
2001b) paleosols have shown that buried paleosols
lose up to an order of magnitude of organic carbon
soon after burial in well-drained soils, whereas water-
logged (hydromorphic) or peaty paleosols show sig-
nificantly less to no loss of organic matter (Stevenson,
1969). Given their red color and low ferrous to ferric
ratios (see Fig. 6), much of the iron in these paleosols
has been oxidized, indicating at least a moderatedegree of aeration post-burial, and oxygen promotes
the breakdown of organic matter. This likely accounts
for the dearth of detectable organic matter.
Sheldon and Retallack (2001) showed that the
degree of compactibility varies according to the initial
physical properties of the soil. Regional stratigraphic
relationships indicate a burial depth of 2–4 km, so the
paleosols have been compacted to between 61.2% and
87.8% of their original thickness depending on burial
depth and soil order (see Sheldon and Retallack,
2001). Given that all of these paleosols are developed
on alluvium, an estimate based on inorganic flood-
plain silts and muds (see Sheldon and Retallack,
2001) of 78.6–86.4% of the original thickness is a
good first order generalization for the sedimentary
succession as a whole.
6. Paleoclimatic reconstruction
A number of means have been devised to recon-
struct paleoclimate from paleosols. Retallack (1994)
has suggested that the depth to the Bk horizon can be
related to mean annual precipitation (see Royer (1999,
2000) and Retallack (2000) for discussion of this
approach). Although a couple of the Sardinian paleo-
sols effervesce slightly when hydrochloric acid is
applied, there is nothing that would qualify Bk ho-
rizons (Soil Survey Staff, 1998). Royer (1999) sug-
gested that soil carbonate is absent in regions
receiving precipitation N760 mm per year, although
this value varies with seasonality and local evapo-
transpiration (Retallack, 2000; Royer, 2000). Thisvalue for the western US may be applicable to the
Sardinian paleosols given their formation within a
continental interior montane basin.
A more quantitative approach is to compare the
precipitation regimes of modern soils with indices of
chemical weathering (Sheldon et al., 2002; Sheldon,
2003). Climatic transfer functions applied to a set of
paleosols spanning the Eocene–Oligocene boundary
produced results that were consistent with indepen-
dent estimates of mean annual precipitation and mean
Table 3
Paleoenvironmental interpretation
Pedotype Paleoclimate Former vegetation Paleotopography Parent material Timea
Cala Viola Humid (1300–1500 mm/yr)temperate
Eutrophic forest Negligible, but well-drained siltstones
Alluvial sandstones,and mud-stones
1000–10000 years
Lago di Baratz Insufficiently developed to
determine, but probably
humid
Stream-side early
successional woody
and herbaceous vegetation
Negligible, but poorly
drained
Coarse sandstone 100–5000 years
Mácchia Humid (1300–1500 mm/yr)
temperate
Eutrophic forest Negligible,
but moderately
to well-drained
Alluvial sandstones,
siltstones, and
mud-stones
500–5000 years
Mosca Pesca Insufficiently developed to
determine
Stream-side early
successional herbaceous
vegetation
Negligible Coarse sandstone b100 years
a Estimated semi-quantitatively after Retallack (1997) and references therein.
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annual temperature (Retallack et al., 2000; Sheldon et
al., 2002; Sheldon and Retallack, 2004). Although the
paleosols in this study are much older, bulk rock
geochemical data for the Sardinian paleosols canalso be used to reconstruct the paleoenvironmental
conditions under with they formed, because the pres-
ence of root traces, rhizoliths, and burrows indicates a
formerly vegetated landscape for which modern ana-
logues can be identified. Mean annual precipitation
can be related to the chemical index of alteration
without potash as follows (Sheldon et al., 2002):
MAP in mmð Þ ¼ 221:12e:0197 CIAK ð Þ ð3Þ
with an R2= 0.72 where CIA K is 100 times the
molar rat io of aluminum to aluminum, calcium, andsodium (Maynard, 1992). Mean annual temperature
can be related to salinization (Retallack, 1997) where
MAT 8Cð Þ ¼ 18:5 S ð Þ þ 17:3 ð4Þ
with a somewhat low R2=0.37 (Sheldon et al.,
2002). As shown in Fig. 7, mean annual precipitation
increased slightly from 1300 mm/year to about 1500
mm/year, while mean annual temperature increased
slightly but held fairly steady at 11–14 8C. That
result is consistent with the general lack of soil
carbonate. Two analyses (CV22 and CV25 on
Table 1) of Bt horizons are excluded from the anal-
ysis because of extremely low oxide totals owing to
high volatile contents (LOI on Table 1; 26.7 and
14.2%, respectively).
At the present time, soils forming under conditions
of N1200 mm/year mean annual precipitation and 11–
14 8C mean annual temperature are found in Mexico
on the eastern side of the Gulf of California, in theUnited States on the eastern side of the Appalachians,
northern India, Greece, and southern Italy (FAO,
1971–1981). Given the proximity of the Sardinian
paleosols to the Hercynian chain and their low paleo-
latitude (10F5 degrees), northern India is probably
the best modern analogue. Such comparisons are im-
perfect modern analogues because Permo–Triassic
CO2 levels far exceeded present levels (Berner and
Kothavala, 2001; Retallack, 2001c). Nevertheless, it is
clear that these soils did not form in desert conditions.
Could they have instead formed in a monsoonal paleoenvironment?
Modern monsoonal environments are characterized
by extreme seasonal variation, with a pronounced dry
season or seasons, and a short, very wet season or
seasons. There are two main varieties, namely, wet
monsoons as in Southeast Asia, Indonesia, northeast-
ern Australia, and some of India, and dry monsoons as
in central Asia, parts of India, northwestern Australia,
the Arabian peninsula, and the southwestern United
States, however, there is a spectrum of conditions
between the main end-members. Soils forming under
dry monsoonal conditions are most often Vertisols,
Aridisols, and rarely, Mollisols (FAO, 1971–1981).
Soils forming under wet monsoonal conditions are
most often Ultisols or Vertisols (FAO, 1971–1981).
Fig. 7. Paleoprecipitation and paleotemperature estimates using transfer functions from regression of climatic data against chemical composition
of Quaternary soils. The standard error on the precipitation estimate is F182 mm and the standard error on the temperature estimate is F4.4 8C.
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Only the Cala Viola and Mácchia pedotypes are
sufficiently developed to use in comparisons with
modern environments. Both pedotypes developed
on areas of little or no topographic relief, had similar
parent material, and indicate similar paleoclimatic
conditions (Table 3). The primary differences wer e
formation time and vegetative covering (Table 3),
though it could be argued that Cala Viola pedotypes
represent later stage succession of Mácchia pedo-
types, however there is not sufficient evidence to
conclude this robustly.
A dry monsoon is considered first. In Vertisols,
large precipitation differences or seasonal soil mois-
ture deficits between wet and dry seasons change the
physical volume of smectite clay minerals in soils.
During the wet season, clays swell with the addi-
tional water. In the dry season, the clays lose the
water that they have gained and the parting between
layers shrinks. These shrink-swell cycles lead to
deep cracks in the soil. The behavior of the clay
minerals and colloids also gives rise to mukkara
structure and gilgai microrelief that readily distin-
guishes Vertisols (Coulombe et al., 1996; Coulombe,1997; Retallack, 1997; Driese et al., 2000, 2003).
None of these features (deep vertical to sub-vertical
cracks, mukkara structure, gilgai microrelief) are
present in any of the Sardinian paleosols (Table 4).
Nor do the Sardinian paleosols have pedogenic cal-
crete and salts of Aridisols, or the abundant crumb
peds, organic matter, and fine root traces of Molli-
sols (Table 4).
Wet monsoons are characterized by Vertisols and
Ultisols. Ultisols are similar to Alfisols; the primary
difference is in base saturation. Alfisols are base-rich
soils that typically have forest vegetation, while Ulti-
sols are base-poor forest soils. Because of this diffe-
rence, modern Alfisols and Ultisols are distinguishedon the basis of their base status (e.g., percentage base
saturation), which is not always recorded (or measur-
able) in paleosols. A statistically significant method of
differentiating Alfisols from Ultisols has been derived
for paleosols. The B horizons of Alfisols have molar
ratio of bases (CaO, Na2O, MgO, K 2O) to alumina
(Al2O3) greater that 0.5, whereas the B horizons of
Ultisols have base /alumina ratios less than 0.5, typi-
cally much less (Sheldon et al., 2002). Fig. 8 shows
the base/alumina ratios of paleosols in the Cala Viola
section; most have base/alumina ratios greater than0.5, thereby confirming the field diagnosis of these
paleosols as Inceptisol-like (Mácchia) and Alfisol-like
(Cala Viola) rather than Ultisol-like. Only one of Cala
Viola paleosols plots within the Ultisols field, though
others are bnear-Ultic, Q perha ps indicating some weak
monsoonal influence (Fig. 8).
Retallack (1991a) studied Miocene monsoonal
paleosols and soils of Pakistan and found that they
typically have concretions (rather than nodules) of
hematite, calcite, or interlayered calcite and hematite,
and diffuse carbonate in small nodules throughout the
profile, including the A horizon. There is essentially
no carbonate in the Sardinian paleosols and the rare
Fig. 8. Molar ratio of total bases to alumina for Cala Viola paleosols.
Only one Cala Viola paleosol (at 24.9 m) plots within the Ultisol
field, though others are bnear-Ultic. Q
Table 4
Paleoclimates compared
Features Desert Wet
monsoon
Dry
monsoon
Cala viola
Salts Yes No No No
CaCO3 nodules Yes No Yes No
MAP (1300–1500 mm) No Yes Maybe Yes
MAT (11–148) No Maybe Maybe Yes
Soil Types Aridisols Ultisols Vertisols Alfisols
Vertisols Aridisols Inceptisols
Mollisols Entisols
Layered
Fe(OH)3 –CaCO3
No Yes Yes No
Mukkara/gilgai
gilgai
No Yes Yes No
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observed nodules are unlayered, and silica- or iron-
oxyhydroxide cemented. There are no nodules or
concretions consistent with a monsoonal paleoclimate.
Taken together, these various lines of evidence sug-gest that the Sardinian paleosols were not subject to a
strongly monsoonal paleoclimate, either wet or dry
(Table 4).
Although the Lago di Baratz and Mosca Pesca
paleosols of the Lago di Baratz section show little
significant reddening, the Mácchia and Cala Viola
paleosols of both the Lago di Baratz and Cala Viola
sections are both characterized by very red color.
Intensity of color and degree of clay remobilization
are two-fold indicators of development, and can be
supported with chemical and petrographic data. Degreeof drainage also plays a role in soil color and can be
inferred from the degree of chemical gleization (molar
ratio of Fe2+ / Fe3+), soil redoximorphic features (e.g.,
reduction spots, grey/green paleosols with red mot-
tles), and trace fossils of organisms requiring oxygen
(animal burrows and root traces). The red paleosol
types (Mácchia and Cala Viola) are characterized by
low gleization ratios (e.g., Fig. 6) and nearly uniform
red color, with the exception of rare drab-haloed root
traces. Drab-haloed root traces are commonly created
by micro-reducing conditions, which occur around
decaying organic matter shortly after burial (Retal-
lack, 1991b), and as such, would be unrelated to the
past water table depth. There are no other soil re-
doximorphic features (iron-manganese nodules, ferric
nodules) and the deeply penetrating root traces and
burrows (Fig. 4C–D) indicate good drainage as does
the degree of chemical weathering and clay illuviation
into subsurface horizons. The root traces are drab
from the inside out, as in surface water gley, rather
than groundwater gley, yet there is no high density or
impermeable layer within the paleosols that would
perch the water table.The sequence, as a whole, goes from weakly de-
veloped grey paleosols to more strongly developed
red paleosols, which is consistent with a dropping
base level or increased distance from a stream
(Kraus, 1999), and has no evidence significant paleo-
topography (Table 3). The Cala Viola Nord section of
red paleosols is capped by a thick, areally extensive
conglomerate with centimeter-sized, well-rounded
cobbles that may represent a sequence boundary be-
cause the overlying paleosols in the Cala Viola Sud
section are again weakly developed (Retallack, 1998;
Kraus, 1999). This suggests a long-term cyclicity in
the alluvial delivery system that could be related to
either tectonics or minor climate change, but not todesertification or monsoonal conditions. The red color
of these paleosols appears to be primarily related to
the hydrological conditions in which they formed.
7. Conclusions
Continental red beds should be studied outcrop by
outcrop as they can form in a variety of settings, rather
than generalized to a single genetic model. Red paleo-
sols form in environments ranging from tropical fo-rests to deserts. Red color, in and of itself, is not
diagnostic. Paleoclimatic reconstruction of Late Perm-
ian paleosols on the basis of the degree of chemical
weathering and pedological features indicates humid,
temperate conditions with no evidence of either desert
conditions or precipitation seasonality pronounced
enough to be called a monsoon. The change from
grey paleosols to red paleosols is attributable to
changes in hydrological drainage, rather than desert-
ification or increased seasonality. Low latitude Late
Permian paleoclimate of Sardinia was warm, tempe-
rate and perhaps mildly seasonal, but certainly not
desertic or strongly monsoonal.
Acknowledgements
The author would like to acknowledge financial
support from a Geological Society of America student
research grant to him for this project while he was a
Ph.D. student. An earlier version of the manuscript
benefited from reviews by Steve Driese and Greg
Retallack, and this version has benefited from twoanonymous reviews and a review by Lee Nordt.
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