ale

c

. S

of Lo

ed fo

upon which to base paleoclimatic interpretations.

Early research on modern red deserts supported the

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-

Palaeogeography, Palaeoclimatology, Palaeoeinterpretation that ancient red beds formed in hot, dry1. 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 (Kutzbach

and Gallimore, 1989). The question to be addressed

herein is whether red color alone is sufficient evidence

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 derived

their red color from well-drained, warm conditions

during Pleistocene pluvials, so the red color is relictAbstract

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 PermoTriassic 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; MonsoonDo red beds indicate p

A Permian

Nathan D

Department of Geology, Royal Holloway University

Received 27 September 2004; received in revis0031-0182/$ - 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: n.sheldon@gl.rhul.ac.uk.oclimatic conditions?:

ase study

heldon*

ndon, Egham, Surrey TW20 0EX, United Kingdom

rm 25 February 2005; accepted 16 June 2005

cology 228 (2005) 305319

www.elsevier.com/locate/palaeoeasonal with respectmates that are warm and dry or sto rainfall.Q A model put forth by Dubiel and Smoot(1994) suggests that continental red bed formation is

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

CarboniferousPermian 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 Africa 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

n for

f the

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319306Fig. 1. Map showing the location of field sites and stratigraphic colum

sample numbers, and Munsell colour of the sample is to the right oMosca Pesca and Lago di Baratz paleosols and the overlying Macchia pale

X) rather than at the first logged Macchia Rossa paleosol.the Lago di Baratz section, Verrucano Sardo Formation. LB01-15 are

sample number. The exact transition between the lesser developedosols is unknown and may lie in the covered interval (shown with an

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 additiona

limatology, Palaeoecology 228 (2005) 305319 307France, 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 bayQ) (Fig. 1), and are divided it into fourinformal units (Gasperi and Gelmini, 1979). The red

beds described in this paper are from bUnit 2,Q a 150m 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 deposition

on 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 (AnisianEarly

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 an

unknown 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 Macchia paleosols of

the Lago di Baratz section (Fig. 1) represent the first

red beds. If this is the case, given the 7585 m

exposed in the Cala Viola sections (Figs. 2 and 3)

N.D. Sheldon / Palaeogeography, Palaeocand a total thickness of 150 m for Unit 2 (Gasperi and

Gelmini, 1979), there can be no more than a few tenssymbols apply to the right column, which represents the dominan

lithology.,

lt

limatoN.D. Sheldon / Palaeogeography, Palaeoc308of 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

and in contrast to the fluvially-derived sandstones

(Fig. 4B). Many of the paleosols also preserve drab-

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.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 8097% clay and phyllo-

silicate minerals and 320% quartz and lithics (includ-grain size changes (Retallack, 1997). Munsell color

was recorded as well as the qualitative degree of

calcareousness on the basis of reaction with dilute

hydrochloric acid (Retallack, 1997). Samples were

collected for petrography and geochemical analysis

from three sites north of Alghero, near Lago di Baratz

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 methodusing 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)

logy, Palaeoecology 228 (2005) 305319ing feldspars) with an average of less than 10%,

whereas C horizons and other fluvial sediments all

Table 1

Geochemical data

Sample Level

(m)

Reacta Horizon SiO2 TiO2 Al2O3 Feb FeO Fe2O3 MnO MgO CaO Na2O K2O 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 99.7

CV30 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)CIAK Clayeynessd (Pbases/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 22 281 180

LB04D 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)

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319 309

Sample Rho

(g cm3)CIAK Clayeynessd (Pbases/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 24 120 280

30

31

32

28

32

31

29

31

33

32

28

27

30

34

34

21

MgO

Table 1 (continued)

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319310CV10 2.74 96.84 0.21 0.51 0.

CV13 2.74 0.20 0.70 0.

CV16 2.64 0.15 1.37 0.

CV19 2.65 0.17 1.28 0.

CV22 2.76 0.18 6.26 0.

CV24 2.67 0.15 1.56 0.

CV25 2.58 0.13 2.52 0.

CV26 2.82 0.20 16.2 0.

CV27 2.74 96.68 0.21 0.54 0.

CV28 2.54 0.18 0.79 0.

CV29 2.70 96.95 0.20 0.46 0.

CV30 2.72 97.79 0.20 0.43 0.

CV31 2.60 0.13 1.58 0.

CV45 2.69 0.06 5.57 0.

CV46 2.75 0.12 2.08 0.

CV47 2.60 94.67 0.07 0.37 0.

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);

Pbases /Al= (CaO+

tion=(FeO/Fe2O3).e All trace element compositions.have 1535% quartz and lithics, with an average of

about 20%. Many of the fluvial sediments, and two of

the paleosols, have non-calcareous sandy concretions

ranging 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-

Fig. 4. Field and petrographic photos. A) Outcrop photo of the Cala Viola N

the section (arrow). B) Outcrop photo showing the complex fluvial characte

the light colored vertical streaks are rhizoliths and drab-haloed root traces

horizon (arrow). E) mm-scale quartz concretion (sample CV-20). F) Root t

to into the A horizon of the underlying paleosol. G) Laterally discontinuo

ephemerally closer to the surface. H) Thin section of a root trace (sample0.28 1490 11.8 418 94 30 21 153 270

0.38 1081 125 27 25 147 260

0.84 951 92 36 19 237 184

2.97 959 113 42 19 301 196

1.52 537 87 43 10 93 94

1.03 2439 136 33 16 195 163

0.27 2434 142 41 12 306 124

0.22 9654 272 29 nd 31 40

0.24 1485 11.3 507 158 33 24 125 270

0.36 51,452 1017 22 nd 151 178

0.24 1493 12.0 3292 262 32 22 159 244

0.17 1518 12.3 367 179 47 21 173 241

0.31 34,767 688 30 9 269 95

0.79 275 73 34 20 202 79

0.34 303 107 32 22 390 138

1.37 1428 13.4 144 78 17 23 133 102

+Na2O+K2O) /Al2O3; salinization (Na2O+K2O) /Al2O3; gleiza-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):

sj;w qwCj;w

= qpCj;p

ei;w 1 1 1

where qw is the density of the weathered material,Cj,w is the chemical concentration (weight percentage)

of element j in the weathered material, qp is thedensity of the parent material, and Cj,p is the chemical

concentration (weight percentage) of element j in the

parent material. If sj,w=0 (i.e., element w was immo-

ord section; paleosols sit on top of the coarser, horizontal benches in

r of Verrucano Sardo Formation. C) Profile of a Cala Viola paleosol;

(arrows). D) Close-up of vertically oriented burrows in a paleosol A

races (arrow) deep in the C horizon of a paleosol, penetrating nearly

us ground water gleying (arrow) features where the water table was

CV-12).

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319 311

limatoN.D. Sheldon / Palaeogeography, Palaeoc312bile), then ei,w can be solved for separately allowingus to bypass volume (as in the classical definition of

strain) as follows (e.g., Chadwick et al., 1990):

ei;w qpCj;p

= qwCj;w 1 2

where ei,w is the strain on immobile element i in theweathered sample. The parent materials for the profiles

were overbank mudstones and sandstones as appropri-

Fig. 5. Chemical degree of weathering. A) Ca and Sr loss in the type Macch

1 represents 100% loss of Ca relative to the parent material, and a tau vthe Cala Viola type profile showing greater Ca loss, consistent with a grea

more complicated changes, but are still consistent with a greater degree o

geochemistry (CIAK (Maynard, 1992) and clayeyness (molar ratio of alsignificant offset between values low in the profile and high in profile is evi

bbulgeQ consistent with the field identification of a Bt horizon.logy, Palaeoecology 228 (2005) 305319ate, 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 Macchia 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-

ia and Cala Viola paleosols assuming Ti is immobile. A tau value of

alue of 0 represents the parent material. Both paleosols lost Ca, with

ter degree of chemical weathering. Other elements such as Sr show

f chemical weathering in the type Cala Viola profile. B) Additional

umina to silica; Retallack, 1997)). of the type Cala Viola profile The

dence of intense chemical weathering. The clayeyness index shows a

Fig. 6. Gleization for the type profiles of the Cala Viola and Macchia p

(Fe3+) iron.

N.D. Sheldon / Palaeogeography, Palaeoclimatoered, a finding consistent with the field classification of

the paleosols (Table 2). Paleosols generally exhibit the

highest degree of chemical weathering within their A

and 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 btypicalQvalue 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 bayQ)The type Cala Viola paleosol crops out in the

northern Cala Viola section. Cala Viola paleosols areTable 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

Macchia 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 Entisolcomparable 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

BtC, and represent a fairly stable landscape (i.e.,

infrequently flooded; Table 3).

4.1.2. Lago di Baratz (bBaratzs lakeQ)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 AC and represent a frequently

disturbed landscape (i.e., flooded; Table 3).

4.1.3. Macchia (bunderbrushQ)The type Macchia paleosol crops out in the Lago di

Baratz section, and Macchia paleosols are found in

edotypes. Gleization is the molar ratio of ferrous (Fe2+) to ferric

logy, Palaeoecology 228 (2005) 305319 313both field areas. Macchia 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 ped

structure. Macchia profiles are A(Bw)C and repre-

sent a fairly stable landscape (Table 3).

4.1.4. Mosca Pesca (bfly fishingQ)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-

Viola preserve essentially no organic matter (b1%by volume in thin section point counts). Studies of

6. Paleoclimatic reconstruction

tation

ous

es th

limatoQuaternary (Stevenson, 1969) and older (Retallack,

2001b) paleosols have shown that buried paleosolssurface horizons. Mosca Pesca profiles are ACC 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

Table 3

Paleoenvironmental interpretation

Pedotype Paleoclimate Former vegetation

Cala Viola Humid (13001500 mm/yr)

temperate

Eutrophic forest

Lago di Baratz Insufficiently developed to

determine, but probably

humid

Stream-side early

successional woody

and herbaceous vege

Macchia Humid (13001500 mm/yr)

temperate

Eutrophic forest

Mosca Pesca Insufficiently developed to

determine

Stream-side early

successional herbace

vegetation

a Estimated semi-quantitatively after Retallack (1997) and referenc

N.D. Sheldon / Palaeogeography, Palaeoc314lose 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 moderate

degree 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 24 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,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-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 78.686.4% of the original thickness is a

good first order generalization for the sedimentary

succession as a whole.

Paleotopography Parent material Timea

Negligible, but

well-drained siltstones

Alluvial sandstones,

and mud-stones

100010000 years

Negligible, but poorly

drained

Coarse sandstone 1005000 years

Negligible,

but moderately

to well-drained

Alluvial sandstones,

siltstones, and

mud-stones

5005000 years

Negligible Coarse sandstone b100 years

erein.

logy, Palaeoecology 228 (2005) 305319sols 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, althoughthis value varies with seasonality and local evapo-

transpiration (Retallack, 2000; Royer, 2000). This

value 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 EoceneOligocene boundary

produced results that were consistent with indepen-

dent estimates of mean annual precipitation and mean

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 can

also 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 mm 221:12e:0197 CIAK 3with an R2=0.72 where CIAK is 100 times themolar ratio of aluminum to aluminum, calcium, and

sodium (Maynard, 1992). Mean annual temperature

At the present time, soils forming under conditions

of N1200 mm/year mean annual precipitation and 1114 8C mean annual temperature are found in Mexicoon the eastern side of the Gulf of California, in the

United States on the eastern side of the Appalachians,

northern India, Greece, and southern Italy (FAO,

19711981). Given the proximity of the Sardinian

paleosols to the Hercynian chain and their low paleo-

latitude (10F5 degrees), northern India is probablythe best modern analogue. Such comparisons are im-

perfect modern analogues because PermoTriassic

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?

N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319 315can be related to salinization (Retallack, 1997) where

MAT 8C 18:5 S 17:3 4with 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 1114 8C. Thatresult 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).Fig. 7. Paleoprecipitation and paleotemperature estimates using transfer fun

of Quaternary soils. The standard error on the precipitation estimate is F18Modern 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, 19711981).

Soils forming under wet monsoonal conditions are

most often Ultisols or Vertisols (FAO, 19711981).ctions from regression of climatic data against chemical composition

2 mm and the standard error on the temperature estimate is F4.4 8C.

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 distinguished

on 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, K2O) 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 than

0.5, thereby confirming the field diagnosis of these

paleosols as Inceptisol-like (Macchia) and Alfisol-like

(Cala Viola) rather than Ultisol-like. Only one of Cala

limatology, Palaeoecology 228 (2005) 305319Only the Cala Viola and Macchia 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 were

formation time and vegetative covering (Table 3),

though it could be argued that Cala Viola pedotypes

represent later stage succession of Macchia 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-

Table 4

Paleoclimates compared

Features Desert Wet

monsoon

Dry

monsoon

Cala viola

Salts Yes No No No

CaCO3 nodules Yes No Yes No

MAP (13001500 mm) No Yes Maybe Yes

MAT (11148) No Maybe Maybe YesSoil Types Aridisols Ultisols Vertisols Alfisols

Vertisols Aridisols Inceptisols

Mollisols Entisols

Layered

Fe(OH)3CaCO3

No Yes Yes No

Mukkara/gilgai

gilgai

No Yes Yes No

N.D. Sheldon / Palaeogeography, Palaeoc316tional 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 primaryViola paleosols plots within the Ultisols field, though

others are bnear-Ultic,Q perhaps indicating some weakmonsoonal 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 Ultiso

field, though others are bnear-Ultic.Q

l

of these paleosols appears to be primarily related to

the hydrological conditions in which they formed.

diagnostic. Paleoclimatic reconstruction of Late Perm-

ian paleosols on the basis of the degree of chemical

Retallack, and this version has benefited from two

anonymous reviews and a review by Lee Nordt.

limatoobserved 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 Macchia 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. Degree

of 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 (Macchia 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. 4CD) 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

N.D. Sheldon / Palaeogeography, Palaeoccobbles that may represent a sequence boundary be-

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N.D. Sheldon / Palaeogeography, Palaeoclimatology, Palaeoecology 228 (2005) 305319 319

Do red beds indicate paleoclimatic conditions?: A Permian case studyIntroductionGeologic contextMethodsEvidence of pedogenesisPedotypesCala Viola (violet bay)Lago di Baratz (Baratz's lake)Mcchia (underbrush)Mosca Pesca (fly fishing)

DiagenesisPaleoclimatic reconstructionConclusionsAcknowledgementsReferences