sheldon 2005 a palaeo 3

8/18/2019 Sheldon 2005 a Palaeo 3

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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.

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305–319306


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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.

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305–319 307


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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,


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,


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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