The Late Permian climate. What can be inferred from ...fluteau/UIA/articles/7_fluteau-pangea-climate.pdf · The Late Permian climate. What can be inferred from climate modelling concerning

The Late Permian climate. What can be inferred fromclimate modelling concerning Pangea scenarios and

Hercynian range altitude?

F. Fluteaua,*, J. Bessea, J. Broutinb, G. Ramsteinc,1

aLaboratoire de PaleÂomagneÂtisme, Institut de Physique du Globe de Paris, 4 place Jussieu, 75252 Paris cedex 05, FrancebLaboratoire de PaleÂobotanique et de PaleÂoeÂcologie, FR3 Ecologie fondamentale et AppliqueÂe, UniversiteÂ Pierre et Marie Curie,

12 rue Cuvier, 75005 Paris, FrancecLaboratoire des Sciences du Climat et de l'Environnement, DSM/CE-Saclay, 91191 Gif sur Yvette cedex, France

Received 9 December 1999; accepted for publication 4 September 2000

Abstract

A major unsolved geodynamic problem is the Permian Pangea plate con®guration at the end of Paleozoic era (around

255 Ma). While consensual geology indicates a plate arrangement close to that of the Jurassic prior to the Atlantic opening

(Pangea A), paleomagnetic data indicates a nearly 3000 km more eastward position of Gondwana with respect to Laurussia,

leading to major plate and relieves reorganisation during Permo-Triassic times (Pangea B). Using an atmospheric general

circulation model (AGCM), we simulate the climatic response to both con®gurations. We also test the fundamental role of

paleo-elevations through sensitivity experiments. Each simulated climate is then compared with the aim of constraining the best

®t to a particular paleogeographic scenario. Main trends of simulated Late Permian climate in agreement with paleoclimatic

indicators are: (1) a warm temperate climate accompanied by a monsoon circulation over the eastern side of Gondwana; (2) a

cold temperate climate marked by strong annual thermal amplitude at high latitudes in Gondwana and in Siberia; (3) an arid belt

in the subtropics over the western side of Gondwana and Laurussia; and (4) strong climatic differences over both hemispheres,

respectively. Main variance is found over Laurussia with a simulated tropical climate while an arid climate is suggested by

paleodata. Simulating different paleo-elevations of the Appalachian and the Variscan fold belts can solve this discrepancy. The

best model±data ®t is reached for a mean altitude of 4500 m in the Appalachians and appears to be dependent of Pangea

con®guration with a southern Europe Variscan range of some 3000 m in a Pangea A con®guration or only 2000 m in for Pangea

B. Taking into account the geodynamic context, we argue that Pangea B appears to be the more probable con®guration. q 2001

Elsevier Science B.V. All rights reserved.

Keywords: Permian; paleogeography; climate modelling; data

1. Introduction

A landmass distribution radically different than

at present characterised the Earth's surface at the

end of the Paleozoic Era. At that time, three huge

continental masses, Gondwana, Laurussia and Siberia

coalesced to form the Pangea supercontinent after a

long and complex collision history marked by the

Palaeogeography, Palaeoclimatology, Palaeoecology 167 (2001) 39±71

0031-0182/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.

PII: S0031-0182(00)00230-3

www.elsevier.nl/locate/palaeo

* Corresponding author. Fax: 133-1-44-27-7463.

E-mail addresses: ¯[email protected] (F. Fluteau),

[email protected] (J. Besse), [email protected]

(J. Broutin), [email protected] (G. Ramstein).1 Fax: 133-169-08-7716.

Alleghanian±Hercynian orogeny. The impact on

climate of this peculiar plate con®guration has already

been investigated using both energy balance models

(Crowley et al., 1987, 1989) and atmospheric general

circulation models (AGCM) (Kutzbach and Galli-

more, 1989; Kutzbach and Ziegler, 1993; Kutzbach,

1994). Pioneering numerical experiments using an

idealised paleogeographical reconstruction of Pangea

have shown that huge seasonal temperature extremes

were induced within the large continent during the

Late Permian (Crowley et al., 1987, 1989; Kutzbach

and Gallimore, 1989). Kutzbach and Gallimore

(1989) found that a strong monsoon circulation was

marked by heavy precipitation mainly along the

Tethys coast, whereas the interior of the continent

experienced an arid climate. However, model±data

comparisons with this model revealed important

discrepancies. For example, the high latitudes of

Gondwana are thought to undergo a large annual

temperature range (Crowley et al., 1989), and parti-

cularly with very cold winter temperatures (2308C).

This appears unlikely because of the presence of

reptiles in southern Africa during that time (Yemane,

1993). This disagreement was further re®ned by a

more realistic paleogeographic reconstruction

Yemane, 1993; Kutzbach and Ziegler, 1993),

accounting for more accurate estimates of land±sea

distribution, paleotopography and intracratonic shal-

low waters. Indeed, Kutzbach and Ziegler (1993)

showed that large lakes partly solves the problem of

excess of continentality in Gondwana, improving

model and paleodata agreement. Nevertheless, major

disagreements with paleodata remain, especially over

Baltica, (European domain North of the Hercynian

Orogeny), where all previous experiments simulate a

tropical humid climate despite the fact that all paleo-

climatic indicators suggest aridity.

Because the con®guration of Pangea, particularly

during Late Permian, remains strongly debated, we

felt that part of the problem could be linked to paleo-

geography,. Indeed, several types of Pangea con®g-

urations have been discussed in the literature (Van der

Voo and French, 1974; Irving, 1977; Livermore et al.,

1986; Matte, 1986; Torcq et al., 1997). They are of

particular interest for our climate problem since they

change the sea±land distribution directly to the south

of Baltica, and may thus strongly affect atmospheric

circulation. Another problem related to paleogeogra-

phy is the estimation of paleo-elevations, which are

poorly documented. It is now well known that this

parameter is of critical importance for climate studies,

as demonstrated by the impact of the relatively recent

uplift of the Tibetan plateau on both global climate

and the Asian monsoon (Kutzbach et al., 1989, 1993;

Ramstein et al., 1997a; Fluteau et al., 1999) or by the

impact of the Pangean mountain belt (Appalachian-

Variscan) during Late Paleozoic (Otto-Bliesner, 1993,

1999).

These reasons lead us to investigate the impact of

different land±sea distributions and different paleo-

elevations of the Appalachian and Variscan ranges

on the Late Permian climate, using an AGCM. More-

over, we also used sensitivity experiments to test the

in¯uence of Appalachian and Variscan elevations on

global and local climates. The simulated climates for

each tectonic/elevation con®guration is compared

with paleodata to determine which computation corre-

lates best with ®eld observations.

2. Description of numerical experiments andboundary conditions

2.1. The climate model

We used the Laboratoire de MeÂteÂorologie Dynami-

que (LMD) Atmospheric General Circulation Model

(version LMD5.3) to perform our experiments

(Harzallah and Sadourny, 1995). This 3D atmospheric

model has been largely employed to investigate future

and past climates, in particular during the last glacial/

interglacial cycle (De Noblet et al., 1996; Masson et

al., 1997; Ramstein et al., 1998), but also for the pre-

Quaternary time (Ramstein et al., 1997a,b; Fluteau et

al., 1999). This particular model version has been

described in different papers (Harzallah and

Sadourny, 1995; Masson et al., 1997) and here, we

summarise its main features. The grid point model

has a standard resolution of 64 points regularly spaced

in longitude, 50 points in the sine of latitude, and 11

vertical levels (8 in troposphere and 3 in stratosphere).

The horizontal resolution at mid-latitude is about

400 £ 400 km. This AGCM includes a full seasonal

cycle but no diurnal cycle. All experiments last 16

years with climatic variables being averaged over

the last 15 years.

F. Fluteau et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 167 (2001) 39±7140

2.2. The boundary conditions

2.2.1. Paleogeography

(a) Plate reconstruction. We have used reconstruc-

tions based on paleomagnetic data, under the assump-

tion of a geocentric axial magnetic ®eld. Recent work

on Permian pole position of, respectively, Eurasia or

Gondwana (Torcq, 1997) did not lend any support to

the presence of a signi®cant non-dipolar components

of the Earth magnetic ®eld during the period. The

paleoposition of Laurussia (North America and

Europe) in the northern hemisphere is accurate: the

Late Paleozoic apparent polar wandering path

(APWP) is de®ned by a large number of well-deter-

mined poles (Van der Voo, 1993). Siberia was at that

time on the way to complete the ®nal steps of its

collision with the Russian platform through the

Urals Mountain belt. Its paleoposition has been

computed using the Siberian Late Permian pole

from the paleomagnetic database of Kramov compiled

in Van der Voo (1993). The southern part of Asia is

constituted by a mosaic of accreted blocks that rifted

away from Gondwanaland [see (SengoÈr and Hsu,

1984; Metcalfe, 1996)]. During the Late Permian,

the Tarim block was situated at subtropical latitudes

and offered strong terrestrial connections with Siberia

and Kazhakstan (Gilder et al., 1996). The North and

South Chinese blocks were in contact through the

Quinling belt but still not ®nally accreted. They

were separated from Siberia by the Mongol-Okhotsk

Oceanic domain, and situated at low paleolatitudes

(Zhao and Coe, 1987; Yang et al., 1991). Paleodata,

however, indicate terrestrial connections with the

Tarim and Mongol blocks (Nie et al., 1990). Their

paleopositions, accurately known, have been deter-

mined using the Permian paleomagnetic data issued

in the compilation of Enkin et al. (1991). A nearly

continuous belt of continental blocks including parts

of Iran, Afghanistan, Tibet and western parts of Indo-

china had just rifted away from Gondwana, and was

located in the southern hemisphere, close to the north-

ern periphery of Gondwana. The paleoposition has

been determined using the reconstructions of Besse

et al. (1998).

Reconstructing the southern land masses is more

dif®cult since paleomagnetic data of Gondwana are

more sparse. Against the classical Jurassic Pangean

assemblage of Wegener (called Pangee A), Irving

(1977) opposed the Pangea B reconstruction: the rela-

tive position of Gondwana with respect to Laurussia

by the end of Paleozoic is not the commonly admitted

Jurassic ®t. Gondwanaland is located more to the east

(South America roughly facing North America). This

reconstruction was based on ancient paleomagnetic

studies acquired in 1960s and 1970s, and often consid-

ered not to ful®l present day standard quality criteria

(poor data collections, no fold test, blanket demagne-

tisation most of the time). Van der Voo (1993) thus

proposed that all the Gondwanan poles for this period

were in signi®cant error. However, this view is pessi-

mistic. Several new paleomagnetic poles in Saudi

Arabia and Argentina for periods between the late

Carboniferous (300 Ma) and the early Triassic

(240 Ma) have been published, and their directions

are very similar to the one of selected best ancient

poles. Combining these poles together led Torcq

(1997) to propose a reliable Gondwana APWP for

these periods of time, which favoured again a Pangea

of type B. Recent survey of Madagascar by Torsvik et

al (1999) reinforce this view.

Clearly, a general agreement has not been reached

on Pangea con®guration, and we decided to use both

reconstructions for our climatic simulations. To

obtain a Pangea of type A, we simply placed Gond-

wana with respect to Laurussia using the ®t para-

meters of Bullard et al. (1965) (Fig. 1a). We have

used the Laurussian/Gondwanan eulerian pole of rota-

tion of Torcq et al. (1997) based on paleomagnetic

poles to reconstruct a Pangea of type B (Fig. 1b).

We have used the same reconstructions of the

Tethysian blocks in either Pangea A or B maps,

with minor longitudinal rearrangements due to the

different relative position of Gondwana (Fig. 1a and

b). The position of these blocks implies in both cases a

narrow Tethys ocean roughly centred on the Equator,

whereas most previous reconstructions suggested a

widely opened Tethys ocean, strewn with isolated

blocks.

(b) Land±sea distribution. During the Late

Permian, the oceanic realm is dominated by the

Panthalassa (Paleo-Paci®c) and by the Tethys Sea

(Baud et al., 1993; Dercourt et al., 1993). In our paleo-

geographic reconstructions, the Tethys sea has a smal-

ler surface than in other reconstructions such as the

one of Ziegler et al. (1997). The Late Permian is also

marked by the presence of epicontinental seas. These

F. Fluteau et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 167 (2001) 39±71 41


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(a) Pangea A paleogeography

(b) Pangea B paleogeography

Laurussia

Tethys

Tethys

Siberia

Siberia

Tarim

Tarim

North China

North China

SouthChina

SouthChina

Gondwana

Gondwana

LaurussiaBaltica

Baltica

Panthalassa

Panthalassa

Gondwana

Gondwana

Fig. 1. Paleogeographic reconstructions for Late Permian times: (a) in a Pangea A con®guration; and (b) in a Pangea B con®guration; vertical

scale in meters.

basins were mostly located in the subtropics and in the

mid-latitudes of the northern hemisphere and were

generally characterised by an evaporitic sedimenta-

tion such as in the Zechstein sea (Kiersnowski et al.,

1995) and a mixed evaporitic-terrigeneous sedimenta-

tion as in the Urals and Arctic seaways (Glennie,

1987). In the Southern Hemisphere, a broad intracra-

tonic sea was located in the Parana Basin (SimoÄes et

al., 1998; Zalan et al., 1991) and in the Karoo basin

(Smith et al., 1998) in western Gondwana. The size of

this sea is reduced to a very small area by the end of

the Upper Permian. The huge (and perhaps overesti-

mated) area ¯ooded by this intracratonic sea should

represent its con®guration at the beginning of the

Upper Permian. This sea, connected to the Pantha-

lassa during the early Permian became isolated

because of the Gondwanides orogeny. The fact that

we take these seas or seaways into account, has impor-

tant consequences on the Late Permian climate, as

suggested by Yemane (1993) and Kutzbach and Zieg-

ler (1993). Other inland seas and lakes are not taken

into account by our coarse resolution model.

(c) Paleo-elevations. Estimating the paleoelevation

of mountain belts and their dynamic evolution

remains a dif®cult problem. This point is clearly illu-

strated by the major uncertainties on the formation

processes of the Himalayas or the age of the Tibetan

plateau uplift, albeit both events are younger than

20 Ma (Molnar and England, 1990). The Upper

Permian times post-date the major Hercynian

orogenic phases (Arthaud and Matte, 1977; Dallmeyer

et al., 1986). This orogeny began locally as early as

the Middle Devonian in some areas in response to a

generalised collision context between Laurussia and

Gondwana from the Southern Appalachian to the

Urals. This continent±continent collision led to an

important crustal shortening during the Alleghanian

(in North America) or late Variscan (in Europe)

tectonic compression phases which culminated at

the end of the Carboniferous (Dallmeyer et al.,

1986; Matte, 1986). The collision of the Siberian

plate with Europe began during the Early Permian at

the latest, and important shortening occurred during

the Triassic. The remnants of large parts of the Hercy-

nian range have been reworked by further alpine

tectonics and the opening of oceanic domains, such

as the Tethys and the Atlantic. The volume of sedi-

ment derived from erosion remains unknown and

cannot constrain the long tectonic history of these

ranges.

The altitudes can be guessed from the crustal thick-

ening derived from very uncertain estimates of the

shortening. The elevation of the Appalachians, for

example, led to rather different values ranging from

2±3 km (Faill, 1998) to 6±7 km (Levine, 1986). The

Variscan range has probably experienced a tectonic

evolution similar to that of the Himalayas and Tibetan

plateau in Asia, marked by an important crustal short-

ening [larger than 600 km according to Matte (1986)]

leading to high orography. Becq-Giraudon and Van

Den Driessche (1994) have proposed a high altitude

plateau (5000 m) during late Carboniferous on the

basis of periglacial sedimentation at low latitudes

(08±108N) and a post-tectonic phase of collapse

during the Autunian. A low elevation of less than

500 m is thus proposed for the Late Permian.

However, this last estimate is uncertain, the sea

level altitude not being reached before the mid-Trias-

sic for the basins of the southern Variscan fold belt,

while ®rst evidences of marine sedimentation date

from the Jurassic in the Appalachian (Olsen et al.,

1996). In both cases, this is a quite long time after

the main compression phases. We therefore took

these uncertainties into account in our numerical

experiments in testing several elevations and plate

reconstructions (Table 1) in order to investigate

which con®guration ®ts better the observed climatic

constraints.

2.2.2. Other boundary conditions: sea surface

temperature, vegetation, CO2, orbital parameters and

solar constant

No global data set of sea surface temperature (SST)


Table 1

The set of experiments

Experiment Pangea Mountain elevation (km).

Appalachian Variscan Ural

PA1 A 2.5 0.5 3

PA2 A 4.5 0.5 3

PA3 A 4.5 3 3

PA4 A 4.5 1 3

PB1 B 2.5 1 3

PB2 B 4.5 3 3

PB3 B 2.5 0.5 3


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(a) Mean temperature in DJF ( C)

(b) Mean temperature in JJA ( C)

Fig. 2. Simulated mean surface air temperature (8C) in DJF (a) and JJA (b) at Late Permian using a Pangea A con®guration with a moderately

elevated Appalachian range. Isolines: from 2158C to 408C, contours every 58C, continuous contours for positive temperatures and dashed

contours for negative temperatures; the dark grey area represents temperatures below the freezing point; light and medium grey colours indicate

temperature above 208C.

is available for the Late Permian. Marine faunas and

lithology on the continental margin (in shallow water)

do provide, however, a rough estimate about the large

temperature trends. Warm SSTs marked by fusilinids,

conodonts and corals, stretch along the Gondwanan

coast in the Tethys sea and around South China (Dick-

ins et al., 1993; Brakel and Totterdell, 1993; Kawa-

mura and Michiyama, 1995). Large carbonate

platforms found in Greece suggest warm SSTs in

the western Tethys (Baud et al., 1993)., The Late

Permian high latitudes are marked by cold-water

faunas (Brakel and Totterdell, 1993) and by evidence

of dropstones and glendonites (Bembrick, 1980;

Caputo and Crowell, 1985; Parrish et al., 1996).

Taking these elements into account, we have chosen

to prescribe water temperature of about 258C at low

latitudes in the Panthalassa Ocean and in the Tethys

Ocean and cold water close to 08C at high latitudes.

This SST distribution leads to a pole-to-equator gradi-

ent close to the present day one. Prescribing this SST

gradient at all longitudes leads to a zonal SST distri-

bution. We consider that there are no ice sheet and no

sea ice during the Late Permian although ice marine

deposits are known in Siberia (Epshteyn, 1981). We

use a `no-ice' boundary condition for all experiments,

and only account for changes in land±sea distribution.

The speci®ed SSTs in our experiments are slightly

cooler at both low and high latitudes than those

depicted by Kutzbach and Ziegler (1993).

The LMD AGCM includes a sophisticated soil-

vegetation model (SECHIBA) (DucoudreÂ et al.,

1994), distributed into eight different biomes (tropical

forest, caduceus forest, savanna, sempervirens,

meadow, tundra, steppe and desert). For the Late

Permian, the paleobotanic data do not permit an accu-

rate reconstruction of the vegetation at a global scale.

Therefore, we use a ªtransferº function based on a

present day (PD) calibration to assign a biome distri-

bution to each grid. This transfer function is calibrated

on the present day and computes the percentage of

each biome in each grid cell according to the latitude

and the elevation of the grid point. The distance of the

grid point to the sea is not taken into account to recon-

struct the vegetation.

We prescribe a CO2 atmospheric content three

times higher than at present (900 ppm). This value

agrees with the modelled curve of Berner (1992)

and is less than that used by Kutzbach and Gallimore

(1989) and Kutzbach and Ziegler (1993). They used

CO2 concentrations ®ve times higher than at present.

Orbital parameters (precession, obliquity, eccentri-

city) are set to present values. We also keep the

solar constant unchanged at the top of the atmosphere

(1365 W/m2) although a possible decrease of around

1% was used in Kutzbach's experiments (Kutzbach

and Gallimore, 1989).

3. The AGCM results

3.1. The Late Permian climate, the case of Pangea A

In the ®rst experiment, we used a Pangea A recon-

struction with a moderately elevated Appalachian

mountain range of about 2.5 km and no signi®cant

relief in the Variscan mountain range (0.5 km) in

southern Baltica (Faill, 1998; Becq-Giraudon and

Van Den Driessche, 1994). The main features of the

Late Permian climate are at ®rst, extremely hot

summer temperatures in the subtropics, reaching

some 408C in northern Gondwana (Fig. 2a) and

more than 308C over Laurussia (Fig. 2b). Temperature

varies as a function of the continent surface area. For

Laurussia and Siberia, the fragmentation caused by

the Arctic (Zechstein) and Urals seaways limits

summer warming. Nevertheless, this warming is

strong enough in both hemispheres to generate deep

thermal low-pressure cells (Fig. 3a and b). These

troughs, located in the summer hemispheres, advect

moisture from the Tethys Sea leading to a monsoon

type circulation, which generates heavy precipitation

over northern Africa, Arabia, up the northern edge of

India and Australia in December, January, February

(DJF), and over southeastern Laurussia in June, July,

August (JJA). Summer monsoon circulation is

replaced by winter westerlies over Gondwana (Fig.

4b), carrying moisture from the Panthalassa Ocean

and from a huge inland lake in western Gondwana

to the mid-latitudes (Fig. 3b). The presence of numer-

ous lakes in Gondwana, probably underestimated in

our reconstructions, may have played a key role at the

Late Permian (Yemane, 1993, 1996; Kutzbach and

Ziegler, 1993). However, only a thin belt, less than

2000 km wide centred at mid latitudes in each hemi-

sphere, undergoes winter precipitation (Fig. 4a and b).

In the northern hemisphere, winter westerlies affect



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-15.0

-15.0 -15.0

0.0

0.0

10 m/s

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Sea level pressure (hPa) and wind at 850 hPa (m/s) in DJF

(b) Sea level pressure (hPa) and wind at 850 hPa (m/s) in JJA

Fig. 3. Simulated atmospheric circulation in DJF (a) and JJA (b). Sea level pressure (hPa-1000) and winds at 850 hPa (1500 m); continuous

(dashed) lines represent isobars above 1000 hPa (under 1000 hPa) and the vectors show the amplitude and orientation of the wind.


.00

1.00

2.50

5.00

7.50

10.00

20.00

40.46

2.5

5.07.5 1.0 1.0

1.0

2.5

2.5

2.52.5

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

1.0

2.5

2.5

2.52.5

2.5

2.5

2.52.5 2.5

5.0

5.02.

5 2.5

2.5

7.5

2.5

2.5

1.0

1.0

5.05.0

1.01.0

1.0

1.0 1.01.0

1.0

2.52.52.5

2.52.5 2.5

1.07.5

7.5

10.010.0

1.0

1.0

5.07.5

5.05.0

20.0

5.0

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

.03

1.00

2.50

5.00

7.50

10.00

20.00

30.50

2.5

2.5

2.5

2.5

2.5

2.5

2.5

5.07.510.0

1.01.0

1.0

1.0

1.0

1.01.0

1.0

1.0 1.0

1.01.0

1.0

1.0

1.0

1.0

5.0

1.0

1.01.0

1.0

2.52.52.5

2.5

2.5

2.5

2.5 2.5

5.0

5.0 5.07.5

2.5

2.5

2.5

2.52.5

2.5

2.5 2.5

7.5

7.5

10.0

10.0 10.0

5.05.0

2.5

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean precipitation in DJF (mm/day)

(b) Mean precipitation in JJA (mm/day)

Fig. 4. Mean precipitation (mm/day) in DJF (a) and JJA (b). White areas receive less than 1 mm/day; dark grey areas receive more than 10 mm/

day.

only the extreme northern part of Laurusia, while

most of Baltica receives precipitation due to a winter

monsoon circulation (Figs. 3a and 4a).

Higher latitudes experience extremely cold tempera-

tures (Fig. 2a and b), down to 2158C over southern

Gondwana (mainly Antarctica) (Fig. 2b) and 2108Cin northern Siberia (Fig. 2a) and thus experience a strong

annual thermal amplitude. The subtropics are marked by

warm temperatures and by very low precipitation rates

(Fig. 4a and b). Precipitation is nearly absent during

winter in this area, with huge arid zones, that are mainly

located over western Pangea (monsoon circulation

affects the eastern side).At low latitudes, precipitation

is associated to the inter-tropical convergence zone

(ITCZ) which experiences a seasonal excursion over

northeastern Gondwana (Fig. 4a and b). The ITCZ is

located over the Appalachian range in JJA, and shifts

southward over northern Gondwana in DJF. This latitu-

dinal excursion follows the seasonal swing of the maxi-

mum incoming solar radiation. Climate of the

continental blocks located in the Tethys Ocean are

driven by their latitudinal position and by the prescribed

sea surface temperature in the experiments. The North

China and Cimmerian plates receive precipitation (Fig.

4a and b) carried by the easterlies during summer (Fig.

3a and b) whereas South China, located at the equator,

receives precipitation nearly year-round (Fig. 4a and b).

This simulated atmospheric circulation is relatively

close to Kutzback's experiment (Kutzbach and Ziegler,

1993). Local differences result from local differences in

paleogeography.

The annual mean Late Permian temperature aver-

aged over land is 68C warmer than the present simu-

lated with the same AGCM. The different

paleogeographic con®guration, the absence of ice

caps, and higher CO2 atmospheric content are the

main reasons for warmer temperatures during the

Late Permian. The annual mean precipitation averaged

over land is weaker by 13% (0.36 mm/day) than at

present. Because of the paleogeography, aridity

spreads largely over supercontinent in the subtropics

and the effect from the SSTs are mainly restricted over

the coastal margins, as Crowley et al. (1987) suggested.

3.2. The climatic changes between a Pangea B and a

Pangea A

The second experiment (PB1) uses a Pangea B

con®guration in which we prescribe a moderately

elevated Appalachian mountain range (2.5 km) as in

the previous experiment (PA1). In southern Europe,

the collision of the Laurussia and Gondwana plates

necessitated by a Pangea B reconstruction led us to

prescribe a mountain range at a signi®cant minimum

altitude of about 1000 m, decreasing slowly from west

to east in southern Baltica.

The climatic differences between Pangea B and

Pangea A result mainly from the difference in relative

position between Gondwana and Laurussia. For

Pangea B, western and eastern Gondwana are, respec-

tively, shifted northward by about 108 and southward

by about 78 with respect to Pangea A. In both recon-

structions, Laurussia remains at the same position.

Thus, only the insolation received by Gondwana is

signi®cantly modi®ed.

3.2.1. Climatic differences over Gondwana

Because western Gondwana is shifted northward in

Pangea B, the annual mean incoming insolation at the

top of the atmosphere over this region is stronger by

about 40 W/m2 than in a Pangea A con®guration.

Conversely, the annual mean insolation is reduced

by around 10 W/m2 over eastern Gondwana in Pangea

B. However, the differences in annual mean insolation

hide a complex seasonal behaviour that results from

the latitudinal pro®les in insolation.

During austral summer (DJF), the location of

Pangea B Gondwana leads to an important climatic

change at low latitudes (Fig. 5a). Northern Gondwana

receives less incoming insolation (212 W/m2,

22.5%). Therefore a statistically signi®cant weak

cooling is observed over northwestern Gondwana

near the northern part of South America (Fig. 5b).

Conversely northeastern Gondwana (north Africa)

experienced a weak warming despite the decrease in

insolation. This apparent contradiction results from

differences in atmospheric circulation between the

two Pangea con®gurations. In Pangea B, the low-pres-

sure cell located over Gondwana strongly reduces the

moisture input from the Tethys ocean. As a result,

cloud cover is decreased, which induces a warming

as a consequence of less insolation at the top of atmo-

sphere and more solar ¯ux at the surface. Precipitation

is therefore weaker over northwestern Gondwana in

Pangea B than in Pangea A (22 mm/day, 240%)

(Fig. 5c). At higher latitudes, more (less) insolation


is received over the southwestern (southeastern) part

in Pangea B than in Pangea A because of the latitu-

dinal shift (Fig. 5a). However, the climatic differences

do not mimic these changes in insolation. There is, in

fact, a strong non-linear response of temperature to

the change in insolation. The insolation is reduced

over the southeastern Gondwana inducing a 38C cool-

ing over a wide area (Fig. 5b).

During the austral winter (JJA), the situation is

completely different. The maximum insolation is

located on the northern hemisphere. The western

Gondwana, which is located at lower latitudes in

Pangea B than in Pangea A, receives more insolation

at all latitudes (33 W/m2, 121%) (Fig. 6a). Eastern

Gondwana, which is located at higher latitudes,

receives less insolation (220 W/m2). The changes in

insolation are more pronounced in winter than in

summer because the latitudinal gradient in insolation

at the top of atmosphere is stronger during this season.

This leads to a warming over western Gondwana

(68C) with a maxima in the subtropics and a cooling

(28C) over a small area in eastern Gondwana (Fig. 6b).

The change in incoming solar energy is strengthened

by a 6% albedo reduction due to weaker snow cover

over the western part. Albedo is an important factor

controlling the climate over the eastern part. For the

whole of Gondwana, winter precipitation (Fig. 6c) are

weakly dependent on the chosen Pangea con®guration

because of its strong aridity.

3.2.2. Climatic differences over Laurussia

The geographic position of Laurussia is the same on

both Pangea con®gurations; therefore, there is no

change in the incoming solar ¯ux received by the

continents to the north of the Variscan and Appala-

chians ranges (Figs. 5a and 6a). We observe climatic

changes over Laurussia due to changes in large-scale

atmospheric circulation induced by the differences

between Pangea con®gurations.

Over the Baltica low lands, we observe a 28Csummer warming (Fig. 6b). Precipitation is strongly

reduced by 1.1 mm/day (265%) in winter and 1 mm/

day (250%) in summer (Figs. 5c and 6c) leading to a

drier Baltica in Pangea B. For Pangea B, the dryness

results from both the position of the austral summer

low pressure over northeastern Gondwana, which

implies a de¯ection of moisture ¯ux and the presence

of a 1000 m. high mountain range in the south of

Baltica, which blocks the southerly moisture ¯ux.

The process implying the Gondwana low-pressure

cell is ef®cient in winter (austral summer), whereas

the second mechanism implying the mountain range

occurs year round, although its impact is stronger in

summer (austral winter). The lowering of moisture

input over Europe decreases cloudiness by 15% in

summer, strengthening the incoming solar radiation

at the surface by 20 W/m2 (15%) and inducing warm-

ing of Baltica.

3.3. Sensitivity experiments to mountain elevations

3.3.1. In¯uence of changes in Appalachians elevation

in Pangea A (PA2)

In this section, we present climatic differences and

the changes in atmospheric circulation induced by

increasing the mean elevation of Appalachian by

2000 m. in a Pangea A con®guration. Because this

mountain range is located close to the equator, the

region of strongest incoming solar ¯ux is located

north of the range in JJA and to the south in DJF.

This leads to a seasonal reversal of the atmospheric

circulation.

The change in elevation leads to a cooling of some

148C in both seasons over the Appalachians (Figs. 7a

and 8a). Most of the cooling is due to the high topo-

graphy (about 128C using a 68C/km lapse rate). The

cooling induces snowfalls in JJA over the highest grid

point. Albedo feedback also explains a part of the

cooling. Precipitation increases over the mountain

range by 8 mm/day in winter (Fig. 7b) and 10 mm/

day in summer (Fig. 8b).

The adjacent lowlands are also sensitive to these

elevation changes. During winter (DJF, austral

summer), northern Gondwana undergoes a warming

of some 48C (Fig. 7a) and a decrease in precipitation

(22.5 mm/day) (Fig. 7b), whereas southern Laurussia

experiences no signi®cant change. During summer

(JJA, austral winter), we observe the opposite trend.

Southern Laurussia becomes warmer (3.58C) (Fig. 8a)

and drier (22.3 mm/day, 265%) (Fig. 8b) whereas

there is only a weak cooling of about 18C in north-

western Gondwana

The climatic trends over the adjacent areas are

linked with changes in atmospheric circulation due

to the elevation of the Appalachian fold belt. The

meridional wind component reveals a change in



advection. Indeed, using a low orography, winter

wind blows southward from subtropical Laurussia

toward the Gondwanan low-pressure cell. The

weak precipitation above the Appalachian fold belt

(Fig. 4b) suggests that a low-lying range does not

constitute a signi®cant barrier for air mass. In

contrast, for high standing range, wind blows toward

the Appalachians fold belt from both sides. The

latitude of the range is of critical importance in

this process as Otto-Bliesner suggested (1993,

1999). Wind patterns reverse over the summer

hemisphere whereas they remain unchanged in the

winter hemisphere, except that the wind speed is

faster. For a high mountain range, moisture ¯ux is

blocked and must rise, leading to its condensation.

Precipitation then falls over the ¯ank of the moun-

tain and latent energy is released. Convective

motions induced by the released energy leads to

moisture advection on both sides of the range. Climate

becomes dryer over the adjacent lowlands in the

summer hemisphere because moisture is carried

toward the range. This leads to a decrease in precipi-

tation and an increased warming.

3.3.2. In¯uence of changes in Variscan elevation in

Pangea A (PA3)

We speci®ed low elevations in Baltica (about

500 m) in the previous Late Permian simulations

(PA2). However, southern Baltica was subjected to

Hercynian uplift near the Permo-Carboniferous

boundary (Becq-Giraudon and Van Den Driessche,

1994). Because the collapse of this range remains

uncertain, we investigate the climatic impact when

the elevation of the Variscan range is increased up

to 3 km during Late Permian (PA3).

This change in elevation induces a cooling by some

108C (for the highest grid point) (Figs. 9a and 10a)

and stronger precipitation occurs for both seasons

over the Hercynian mountain range (Figs. 9b and

10b). As in the previous experiment, we also observe

climatic changes over the lowlands. However, these

changes are mainly located over Baltica in winter and

in summer, where both seasons exhibit a 18C±1.58Cwarming (Figs. 9a and 10a) and a 2 mm/day decrease

of precipitation (Fig. 10a and b).

The presence or absence of an elevated Variscan

range therefore bears important changes on climate

and atmospheric circulation. However, the impact of

the high Variscan range is different from that of the

high Appalachian chain because of the position of the

mountain range and the type of atmospheric circula-

tion involved.

Precipitation over Baltica results from winter and

summer monsoon circulation (Fig. 3a). A high Hercy-

nian mountain range blocks moisture, which

increased precipitation over its southern ¯ank and

leads to a rain shadow effect to the north of the

chain. Less moisture carried over Baltica low lands

leads to a decrease in cloudiness, less precipitation

and warming. Higher elevation of the Hercynian

mountain range enhances the advection of moisture

over the southern ¯ank but it does not modify deeply

the atmospheric circulation because the range is

located in the subtropics. Conversely, in response to

higher Appalachian elevation, we observe a drying of

lowland along the range located in the summer hemi-

sphere. The seasonal swing of the ITCZ disappears

and precipitation is trapped over the mountain

range. This latter effect, which has already been

suggested by Otto-Bliesner (1993, 1999), is largely

due to both the equatorial latitude and the elevation

of the Appalachian range.


Fig. 5. Austral summer (DJF) differences of the following parameters between Pangea B and A: (a) Incoming solar radiation at the top of the

atmosphere (W/m2), scale from blue (less insolation) to red (more insolation).(b) Air surface temperature (8C), scale from blue (cooler) to red

(warmer).(c) Precipitation (mm/day), scale from red (drier) to blue (wetter). The colour scale is a function of the difference. Yellow represents

no change and white shows the areas where differences have not been computed. To highlight climatic changes over Gondwana due to the

Pangea con®guration, we plot the differences in temperature and precipitation on a common map. Climatic differences between two grid-points

on Gondwana are signi®cant only if we make comparisons between two grid-points located in the same reference ®xed to the Gondwana

continent (and not to the latitude/longitude frame which remains unchanged despite changes in con®guration). This is achieved by ªrotatingº

each meteorological ®eld (temperature, precipitation) simulated over Gondwana in a Pangea A con®guration into its corresponding position in

Pangea B using the same ®nite Euler pole of rotation used for the tectonic reconstruction. We then calculate the differences of climatic

parameters between the two (Pangea B climate minus Pangea A climate after rotation). This process is only required for Gondwana, because

Laurasian and Siberian±Kazakhstan blocks are kept ®xed in both Pangea con®gurations. We did not compute such differences for the Tethysian

blocks because their in¯uence on climate are weak in both Pangea con®gurations.


Fig. 6. Same as Fig. 5 but in austral winter (JJA).


-2.5-5.0

0.5

0.5 1.05.0

-0.5

0.5

0.51.0

0.5

-0.5

-0.5

-0.5-1.0

-0.5

-0.5

-0.5

-0.5

-1.0

Max : 7.21

Min : -19.77

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

-0.5

0.5

-1.0

-1.0

0.51.0

2.5

-2.5

-2.5

-0.5

-5.0

0.5

0.51.0

-1.0

0.5 1.0-1.0

0.5

0.51.0

-0.5

Max : 35.70

Min : -9.52

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean temperature difference in DJF ( C) (PA2 minus PA1)

(b) Mean precipitation difference in DJF (mm/day) (PA2 minus PA1)

Fig. 7. Climatic differences in winter in response to different elevations in the Appalachian range in a Pangea A con®guration (PA2 2 PA1): (a)

Air surface temperature (8C). (b) Precipitation (mm/day). Dark grey indicates, respectively, a cooling (a) or an increase in precipitation (b),

light grey indicates a warming (a) or a decrease in precipitation (b). White areas represent changes that do not exceed ^0.58C.


-0.5-1.0

-5.0

-10.0

0.5

1.0

2.5

-0.5

-0.50.5

0.5

1.0

0.5

-0.5

-0.5

Max : 6.69

Min : -19.05

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

-0.5

-2.50.51.0-2.5

-1.0

1.0 0.5

0.5

0.5

0.51.01.0

1.0

1.0 1.0

-0.5

-0.5

-1.0

0.5

Max : 24.34

Min : -14.90

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean temperature difference in JJA ( C) (PA2 minus PA1)

(b) Mean precipitation difference in JJA (mm/day) (PA2 minus PA1)

Fig. 8. Same as Fig. 7 but in summer (JJA).


-0.5

0.5

-0.5

-0.5

-0.5

0.5

-0.5

-1.0

-1.0

-1.0

-1.0

-0.5

-0.5

0.5

Max : 4.26

Min : -15.85

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

-0.5

0.5

0.5

0.5

0.5

0.5

-0.5

1.0

-0.5

0.5

0.5

1.0

-0.50.5

-0.5

-0.5

-1.0

-0.5

-0.5

-0.5

-0.5

Max : 21.56

Min : -4.07

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(b) Mean precipitation difference in DJF (mm/day) (PA3 minus PA2)

(a) Mean temperature difference in DJF (˚C) (PA3 minus PA2)

Fig. 9. Climatic differences during winter (DJF) in response to different elevation of a ªVariscanº range in a Pangea A con®guration

(PA3 2 PA2): (a) Air surface temperature (8C). (b) Precipitation (mm/day). Colour: same as Fig. 7.


0.5

0.5

0.50.5

-0.5

-0.5

0.5

0.5

1.0

-1.0

-1.0

1.0

1.0

-0.5

0.5

0.50.5

Max : 3.08

Min : -22.36

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

0.5

0.5

-0.5-0.5

-0.5

-0.5

-1.0

0.5

1.0

-0.5

-1.0

0.5 -0.5

-0.5 -1.0

-0.5

0.5

-0.5-1.0

0.5

Max : 24.56

Min : -8.03

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean temperature difference in JJA (˚C) (PA3 minus PA2)

(b): Mean precipitation difference in JJA (mm/day) (PA3 minus PA2)

Fig. 10. Same as Fig. 9 but in summer (JJA). Colour: same as Fig. 7.

3.3.3. In¯uence of Appalachians and ªVariscanº

mountain range elevation in Pangea B (PB2)

We now perform sensitivity experiments to moun-

tain elevation using Pangea B con®guration. We

prescribe higher topography for both Appalachian

and Hercynian chains than in the ®rst experience

on Pangea B. The uplifted areas are colder as a

rule (up to 2128C) (Figs. 11a and 12a) and undergo

more rainfall (113 mm/day) (Figs. 11b and 12b) in

both seasons. Like the previous experiments, we

observe climate variations in adjacent lowlands.

However, these climatic changes are sensitive to

orographic changes and they are also a function of

the Pangea con®guration.

In winter, northeastern Gondwana and southwes-

tern Laurussia (located at the same latitude on both

sides of the mountain range) experience cooling (28C)

(Fig. 11a). The opposite trend is observed in summer.

The eastern part of Baltica slightly warms up (Fig.

11a) for both seasons. We only simulate a decrease

in precipitation over southern Laurussia and north-

eastern Gondwana in summer (Fig. 12b).

These climatic changes depend on the Appalachian

and Variscan range elevations. High mountain ranges

strengthen air mass advection and thus, reduce the

moisture available (and the precipitation) in the

lowlands adjacent to the ranges. Elevation changes

induce less pronounced precipitation variations than

in Pangea A. The seasonal shift of the intertropical

convergence zone observed in a Pangea A (PA2) is

not entirely similar to the simulation using Pangea B

with low orography (PB1) (Figs. 11b and 12b).

Indeed, using low elevation for Pangea A (PA1),

moisture is advected by the Gondwanan low-pressure

cell. Conversely, for Pangea B (PB1), this low-pres-

sure cell does not advect moisture because it is located

far away from moisture sources (Panthalassa). Thus,

precipitation remains nearly unchanged over northern

Gondwana in Pangea B despite the change in eleva-

tion. Nevertheless, precipitation decreases signi®-

cantly over eastern Baltica as in the previous

experiment.

4. Comparisons between climate simulations andpaleodata

To make model±data comparisons, we have used

Walter's climatic classi®cation (Walter, 1984),

following previous studies (Ziegler, 1990; Kutzbach

and Ziegler, 1993). This classi®cation is based on

modern biome±climate relationships. The criteria

distinguishing climatic zones are the number of

months with precipitation greater than 40 mm/month

and the growing degree days above 58C, which is

related to vegetation development.

To highlight model±data comparisons, we use

different data sources (lithology, ¯ora, fauna) when-

ever it is possible. It gives a more robust estimation of

climate and it may avoid some climatic pitfalls linked

with preservation conditions (Demko et al., 1998).

Obviously, these data give only a rough estimate of

the climate, which is more qualitative than quantita-

tive. The simulated climate is compared with paleo-

data, that give any information related to temperature

and precipitation (or dryness) and their respective

seasonality (Parrish et al., 1996). In the case of ¯ora,

climatic parameters may be estimated especially from

leaf shape and size and from palynologic assemblage

(comparisons with the nearest living relatives of fossil

taxa are nearly impossible for the Paleozoic) (Wing

and Greewood, 1996). Fossil growth rings highlight

seasonality of precipitation, temperature, or both.

Fauna type also re¯ects environmental conditions

such as sea surface temperature in the case of marine

fossil taxa, or presence or absence of standing water in

the case of amphibians (Parrish et al., 1996). For sedi-

mentary rocks, coal deposits, mostly found at low and

high latitudes, indicate year around precipitation

(without dry season, thus precipitation exceeds

evaporation) but they do not yield any temperature

information (Parrish et al., 1996; Sellwood and

Price, 1996). Reversely, evaporite deposits signify

an excess of evaporation with respect to water input,

which is observed as a rule in the subtropics.

Comparisons between data and simulated climate

using a climatic classi®cation are made more easily in

this way. However, model±data comparison only

shows us whether we can observe consistency/incon-

sistency between simulated climate with available

data at a regional scale. Unfortunately, the data are

unevenly spatially distributed for the Late Permian.

This fact is probably one of the most critical points

of model±data comparisons because we are not sure

that a key climatic area (sensitive to paleogeographic

reconstructions) has been sampled. Finally, we take



-1.0

-1.0

-2.5

-5.0

0.5

0.5

0.5

1.0

-0.5

1.0

1.0

-0.5

0.5

0.51.0

Max : 3.09

Min : -20.15

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

-0.5-0.5

-0.50.5

-2.5

-0.5

0.5

0.5 2.5

-0.5

-0.5

-0.5

-1.0

-0.5

0.5

0.5

1.0

1.0

-0.5

-1.0

0.5

-0.5

-1.0

-1.01.0

1.02.5

0.

Max : 29.66

Min : -22.16

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean temperature difference in DJF (˚C) (PB2 minus PB1)

(b) Mean precipitation difference in DJF (mm/day) (PB2 minus PB1)

Fig. 11. Climatic differences during winter (DJF) in response to different elevation of an Appalachian and a southern Europe range in a Pangea

B con®guration: (a) Air surface temperature (8C). (b) Precipitation (mm/day). Colour: same as Fig. 7.


-0.5

-0.5 -0.5

-1.0

-1.0

-2.5

0.5

1.0

0.5

0.5

0.5

0.5

0.5

-0.5

-0.5

-1.0

Max : 4.93

Min : -20.40

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

1.0 -0.5

-0.50.50.

5

-0.5

0.5

2.5

-2.5

-0.5

0.51.0

-0.5

0.5

0.5

-0.5-0.5 -1.0

0.5 1.02.5

Max : 17.72

Min : -7.66

-180 -120 -60 0 60 120 180

-90

-60

-30

0

30

60

90

(a) Mean temperature difference in JJA (˚C) (PB2 minus PB1)

(b) Mean precipitation difference in JJA (mm/day) (PB2 minus PB1)

Fig. 12. Same as Fig. 11 but in summer (JJA). Colour: same as Fig. 7.

care to compare our simulations with Late Permian

data, although some dating remains uncertain (data may

only be representative of a very short time window).

Despite these dif®culties, we try to highlight model±

data agreements and above all disagreements, the

latter of which are actually more easily observable.

In the ®rst section below, we compare data with

climatic features that are common to both simulations

although the paleogeography is different. In a second

step, the in¯uence of paleogeographic changes will be

discussed.

4.1. The common features of the Late Permian climate

We plot the simulated climate for the experiment

PA1 (Fig. 13a) and PB1 (Fig. 13b). Along the Tethys

coast in the southern hemisphere, the climate is

mainly driven by the summer moisture advection

related to the Gondwana low-pressure cell (Fig. 3a).

This atmospheric circulation is characteristic of a

monsoon climate with important summer precipita-

tion (Fig. 4a), which favours the establishment of a

savannah climate (warm and seasonally humid) in

northeastern Africa and Arabia (Fig. 13a and b). East-

ward, a warm climatic band stretches along the

Tethys. All of our simulations for the Late Permian

in Australia are in good agreement with lithologic and

¯oras evidence that suggest this continent was mainly

characterised by a warm climate belt (which may be

locally dry due to the presence of evaporitic deposits)

along the Tethys coast and a cold climatic belt pole-

ward (Parrish et al.,1996).

In western Gondwana, the simulations PA1 and

PB1 are in a good agreement with paleodata, which

is partially glossopterids due to the presence of the

huge intracratonic sea (Yemane, 1993, 1996; Cuneo,

1996),. However, we do not take into account the

numerous small lakes, especially in Africa due to

the coarse model resolution. This may explain local

disagreements between model results and paleodata.

Northward, the simulated arid climate to the north of

the Parana basin in both experiments is in agreement

with the xeromorphic features of fossil ¯ora in this

area (Cuneo, 1996). Cuneo (1996) also suggests that

growing at high latitudes (Antarctica) are subjected to

a cold humid climate with a signi®cant freezing

period and polar light. A growth under strong seasonal

conditions agrees well with such a climatic condition

during Late Permian in Antarctica, and coincides well

with tree rings in fossil trunks (McLoughlin et al.,

1997). However, despite the coldness of high lati-

tudes, massive coal deposits are found in the eastern

Australian and Indian basins and also in Antarctica

(Cuneo, 1996; McLoughlin et al., 1997). The coal

formation at high latitudes is possible if precipitation

is suf®ciently abundant throughout the year and if the

dry season is relatively short (Retallack, 1995). These

climatic conditions are indeed simulated in eastern

Antarctica, India and Australia in both Pangea con®g-

urations where abundant precipitation occurs in

austral summer (DJF) (Fig. 4a) and is replaced by

snow cover, which prevents the soil from drying in

winter. Thus, the simulated climate ®ts well with the

presence of coal deposits and glossopterids fossil

¯oras in eastern Australia (Parrish et al., 1996).

The geographical proximity of South China, the

Cimmerian blocks and Gondwana (inducing a small

Tethys) explains the mixture of both Cathaysian and

Gondwanan ¯oras in Oman and in Arabia (Broutin et

al., 1995; Broutin et al, in preparation). This is also

supported by the presence of Cathaysian and Gond-

wanan faunas in the Cimmerian blocks (Shi et al.,

1995). Our simulations are in excellent agreement

with paleodata from South China (Fig. 13a and b).

This block is the last area to possess tropical vegeta-

tion (Cathaysian ¯ora) during the Late Permian,

whereas it dominated largely the Laurussian realm

during the Late Carboniferous (Laveine et al., 1987;

Broutin et al., 1995). The presence of a tropical

climate is also supported by the numerous coal depos-

its formed during the Upper Permian (Shouxin and

Yongyi, 1991; Enos, 1995).

The North China block was subjected to a relatively

long rainfall season in its southern part whereas its

northern part is dry. Such a precipitation distribution

is con®rmed by paleodata: presence of Late Permian

coal-bearing beds in the southern part (Shouxin and

Yongyi, 1991) and an Euramerican (Zechstein type

¯ora) dry-adapted ¯ora (Ziqiang, 1985; Poort and

Kerp, 1990; Shouxin and Yongyi, 1991; Enos, 1995)

in the northern part. Northward, the Tarim block is

marked by Angara ¯ora due to its proximity with the

Siberian craton during the Late Permian. Southern

Siberia and Kazakhstan are dominated by a warm

temperate, and humid climate, which is again well

reproduced in our simulations (Fig. 13a and b). In


northern Siberia, the simulated climate also agrees

with paleodata, which one characterised by cold

adapted vegetation. At these high latitudes, precipita-

tion may be suf®cient to favour coal deposition (Zieg-

ler, 1990; Ziegler et al., 1997). The Ural mountains

receive heavy precipitation in all seasons (Fig. 4a and

b) which may explain the large quantities of terrige-

neous sediments ®lling the Ural seaway. Neverthe-

less, these sediments in the Ural basin are also

temperature dependent. The northern Ural basin is


Fig. 13. Simulated climate using a Walter's classi®cation for: (a) Pangea A con®guration (PA1). (b) Pangea B con®guration (PB1). Both

reconstructions use a moderately elevated Appalachian range. Data ± Ze: Zechstein ¯ora (xeromorphic vegetation); Eo: eolian facies; Co: Coal;

Ev: evaporite; Xe: xeromorphic ¯ora; Ca: Cathyasian ¯ora; CaG: Cathasian Gondwanian ¯ora mixture; CaGf: Cathasian Gondwanian faunas

mixture; Eu: euramerican ¯ora (dry adapted ¯ora); An: Angaran ¯ora; AnC: Angaran ¯ora (cold adapted ¯ora); CoT: terrigeneous coal-bearing

sediment; EvT: terrigeneous sediment including evaporitic layers; Tr: tree rings (evidence of seasonality): Gl: glossopteris; Cl: clay assemblage;

Pp: facies indicating periodic precipitation.

mostly composed of terrigeneous coal-bearing sedi-

ment whereas in the south, evaporitic layers are

present. This evaporitic facies also displays a west±

east gradient (Chuvashov, 1995). On the eastern side

of the southern edge of the basin, runoff limits the

formation of evaporitic facies, whereas on the western

margin of this basin, the climate appears to be more

arid and thus, evaporites are more plentiful. Such lati-

tudinal variations are well simulated by our model,

which gives, along the Ural range, a cold climate in

the northern Ural and a warmer yet humid climate in

the southern part. At last, in Laurussia, beside the

huge arid belt in the subtropics, we simulate a warm

climate with rather continuous precipitation through-

out the year in northern Canada, in agreement with

paleodata (Utting, 1994).

4.2. Pangea A versus Pangea B: are climatic

differences supported by data?

From mid to high latitudes in Gondwana, a cold

temperate climate (Fig. 13a) is simulated in PA1,

driven by a large thermal amplitude between the

winter and summer seasons. This climate stretches

over Antarctica, over southern India, and Australia.

A cold temperate climate was also found by Kutzbach

and Ziegler (1993). For PB1, we also simulate a cold

temperate climate despite the latitudinal shift of

Gondwana (Fig. 13b). We have shown in Section

3.2 that this shift in the two Pangea con®gurations

implies locally important seasonal changes in insola-

tion. In response to these changes, temperature

extremes (winter and summer) are modi®ed.

However, the temperature difference between PA1

and PB1 is too ªweakº to simulate two different

climates, de®ned in the climatic classi®cation. It

explains why the middle to high latitudes over Gond-

wana do not exhibit climatic change in response to the

different paleogeographic con®gurations. Actually,

both simulations are in agreement with paleodata

(Fig. 13).

Warm to cool temperate climates are restricted to

middle latitudes (around 458S), between the cold

temperate areas and the subtropical arid belt, from

the Panthalassa coast, southern Africa, and Madagas-

car, to the northern areas of India and Australia (Fig.

13a and b). Warm temperate climate is mainly located

in eastern Gondwana in Pangea A (Fig. 13a) and in

western Gondwana in Pangea B (Fig. 13b). This

difference is obviously driven by the latitudinal shift

of these blocks between the two Pangea con®gura-

tions, which induces temperature changes. However,

in PA1, southern Africa is dominated by warm

climate in its northern part and by cool climate in its

southern part (Fig. 13a). The warm-cool boundary is

located on the mid-latitude precipitation axis,

approximately represented by the position of the jet

stream. Unfortunately, paleodata from southern

Africa (Yemane et al., 1996) and Australia (Parrish

et al., 1996) recorded both warm and cold climatic

phases during the Late Permian. A change in the

paleogeographic con®guration within this period

cannot be excluded, however, the amplitude of this

motion would have been moderate. Other forcing

factors such as orbital parameters (Kutzbach, 1994)

may explain the shift of the warm/cool climatic

boundary within the Late Permian in the mid-latitudes

of Gondwana.

Another large difference created by the model that

allows one to chose between the two Pangea recon-

structions is the climate of northern Gondwana, which

is dry in Pangea A and warm and seasonally humid in

Pangea B. Unfortunately, no Late Permian paleodata

is available for northern Gondwana; accumulation of

such data would thus be highly desirable.

Finally, the only usable signi®cant differences

between Pangea A or B con®guration is situated in

the Baltica region of Laurussia: using a Pangea A

con®guration with a low mountain elevation leads to

a tropical climate over most of Baltica except over

some points bordering the Zechstein Sea (Fig. 14a).

Using a Pangea B con®guration with low relief, we

simulate a drier climate over Baltica (Fig. 14b). The

arid belt increases in size by almost 15% between

these two experiments, stretching from western Laur-

entia to eastern Baltica. Taking Baltica alone, the

increase reaches some 280%.

Comparing these models results with paleodata (see

on Fig. 13a and b), major problems arise in the tropics

and subtropics, and especially the extent of the arid

belt along the Laurussian/Gondwanan suture. In the

case of Pangea A, the result is in total disagreement

with observations. This discrepancy was already

pointed out by Kutzbach and Ziegler (1993) in their

Late Permian climate simulation.

Indeed, paleodata suggest the presence of dry



Fig. 14. Simulated climate using a Walter's classi®cation focused on the tropical area: (a) Pangea A with a moderately elevated Appalachian

range (PA1). (b) Pangea B with a moderately elevated Appalachian range (PB1). (c) Pangea A with an elevated Appalachian range (PA2). (d)

Pangea A with elevated Appalachian and Hercynian ranges (PA3). (e) Pangea B with elevated Appalachian and Hercynian ranges (PB2).

adapted vegetation (coniferous) with pronounced

xeromorphic characteristics in Baltica. This vegeta-

tion known as Zechstein ¯ora has been found in

Late Permian basins of England, Germany, Hungary,

and Russia (Poort and Kerp, 1990; Warrington and

Scrivener, 1990). The Late Permian sporomorph

assemblages in the southeastern Iberian range in

Spain (Doubinger et al., 1990) and in the Moscow

basin (Utting and Piasecki, 1995) also have points in

common features with Zechstein dry-adapted ¯ora.

Araf'ev and Naugolnykh (1998) suggest that the fossil

roots in the Sukhona and Malaya Severnaya Dvina

river basins belong to herbaceous plants, which have

grown in a desert environment marked by periodic

precipitation. The existence of a desert environment

is also supported by the Late Permian lithology, which

formed in intermittent channels and playa lakes. This

lithology has been also observed in the Moscow

Syncline (Araf'ev and Naugolnykh (1998)). All

these data re¯ect an arid climate, which is underesti-

mated in the simulations PA1 and PB1.

In the Pechora Fore-Urals (northeastern Baltica),

the Upper Permian ¯ora is found in grey-coloured

lenses intercalated in red beds (Meyen, 1987). These

lenses are lacustrine in origin, which might have been

produced by periodic precipitation (dry/wet cycle) as

in the Moscow basin. However, the ¯oral assemblage

found in the Pechora Fore-Urals is similar to that of

eastern Greenland (Balme, 1970; Meyen, 1987) but

has some important differences with the Zechstein

¯ora. A sub-Angaran province including eastern

Greenland, Sverdrup basin, Svalbard and the Barents

Sea Shelf is suggested by palynologic assemblage

(Utting and Piasecki, 1995). These different basins

were relatively close in the Late Permian. However,

the Late Permian formations in the Svalbard and

Barents seas also contain Zechstein pollen grains

(Lueckisporites virkkiae) (Utting, 1994). The Flower-

pot formation in Oklahoma in western Laurussia

(from 58N to 308N) possesses vegetation similar to

Zechstein ¯ora (Utting and Piasecki, 1995). Evapori-

tic basins (Anderson et al., 1995) and broad terrestrial

eolian facies (Mazullo, 1995) suggest an arid climate

stretching from the foothill of the Appalachians

(locally over the equator) up to 308N.

In North America, a warm and seasonally humid

belt stretches along the arid subtropical area (Fig.

14a). This makes sense because a dry climate is not

expected so close to the equator (West et al., 1997).

Astronomical parameters or the elevation of the

Appalachians range have been suggested to explain

the arid climate (West et al., 1997). Close to the Arctic

Ocean (Eastern Greenland, Svalbard, Barents Sea

Shelf), these sites experience a warm temperate

climate with relatively well-distributed precipitation.

Such a climate is supported by the existence of a ¯oral

province different from the rest of Baltica (Utting,

1994).

The critical problem of the Late Permian climate

concerns thus the extent of the arid belt at low lati-

tudes. In the case of a Pangea A, the result is in total

disagreement with observations. This discrepancy

was already pointed out by Kutzbach and Ziegler

(1993) in their Late Permian climate simulation. On

the contrary, the dryer characters observed in the PB1

simulation (Fig. 14b) is in much better agreement with

paleodata described above, but its extension is not

suf®cient to completely reconcile the model with the

data. Another forcing factor must thus play a more

signi®cant role, and could be associated with the

poorly constrained elevations of the Appalachian

and Variscan mountain ranges.

4.3. Climatic in¯uences of the mountain elevations

Fig. 14c represents the simulated climate in PA2 for

an elevated Appalachian range (compared with Fig.

14a). Over the highest points (about 4500 m), the

tropical humid climate is replaced by a polar climate

due to perennial snow. This climate may be compared

with that of the Tibetan plateau or the Altiplano in

South America. The vegetation was probably sparse

at high elevations, whereas the presence of heavy

precipitation over the ¯anks may have contributed to

the development of important vegetation. In response

to the atmospheric circulation changes driven by the

mountain orography, we observe an important

increase in aridity by 14% on each side of the Appa-

lachian fold belt (plains). The aridi®cation of western

Laurussia is in agreement with paleodata and may

explain both the observed terrestrial eolian facies

(Mazullo, 1995), and the xeromorphic vegetation,

and may have contributed to the formation of an

evaporitic basin (Anderson and Dean, 1995).

However, the drying does not stretch beyond the eastern

end of the mountain range. Thus, the western and eastern


parts of Baltica were largely humid, which disagrees

with the paleodata. We therefore studied the impact of

an elevated Variscan range along the southern margin

of Baltica, in order to check if the simulated climate

with the paleodata may be reconcilied.

When adding a high Variscan range in Pangea A

(PA3), the Baltica block becomes arid (Fig. 14d), in

better agreement with paleodata. A high Variscan

range maintains and locally increases the aridi®cation

of the subtropics in western Laurussia and northern

Gondwana. Conversely because the Variscan range

receives abundant precipitation year round, the

climate becomes warm and wet over its southern

¯ank. Unfortunately, no paleodata exist to check this

result.

Fig. 14e presents the simulated climate in the case

of high Appalachian and Variscan ranges using

Pangea B (PB2). Not surprisingly, the area subjected

to an arid climate increases along the range in western

Laurussia. This arid climate stretches over the whole

of Baltica up to the Ural seaway. This climate pattern

over Laurussia agrees with the paleodata and is close

to PA3 experiment.

5. Geodynamic consequences of the climate inBaltica

Rainfall is sensitive to Pangea paleogeography,

which in turn implies large differences in the atmo-

spheric circulation. For similar Variscan range eleva-

tion, Pangea B induces weaker precipitation than

Pangea A over Baltica. The presence of an open

ocean (Tethys Ocean) in Pangea A provides more

year round moisture for a same Variscan range eleva-

tion. In Pangea B, the presence of land directly to the

south of Baltica avoids the transport of winter moist-

ure towards the southern ¯ank of the Variscan range

and Baltica. Thus, the effect of an increasing elevation

of the Variscan range in Pangea B acts only to modify

summer precipitation.

Because temperature is warm throughout the year

in both scenarios, precipitation is the key parameter

available to test the climate of Baltica against paleo-

data. The number of months exceeding a threshold

of some 1.11 mm/day has been chosen to character-

ise the intensity of aridity over Baltica. In Pangea A,

climate evolves from a tropical for a low Variscan

range to arid for an elevated range of some 2000 m.

In a Pangea B, an arid climate affects about two

third of the Baltica block as soon as the elevation

of the Hercynian range reaches 900 m.

The aridity of the climate deduced from paleodata

can therefore be used to estimate the elevation of this

range in Pangea A and B con®gurations. We have

plotted on Fig. 15, the annual mean precipitation

over Baltica in function of the mean elevation of the

Variscan range (see the caption of Fig. 15 to have

further details on the method that we used). The

upper limit is reached by the Pangea A curve for an

elevation of 1300 ^ 200 m and by the Pangea B curve

for an elevation of 400 ^ 200 m (extrapolated

curves). The lower limit intersects the Pangea B

curve at 2000 ^ 200 m and the Pangea A curve at

3000 ^ 300 m (the exponential function becomes

tangent to the lower limit for high elevations and

thus increases the uncertainties).

The experiment in a Pangea B con®guration with

an elevated Variscan range implies the largest arid

area stretching all over the Baltica block except for a

few point located along the Arctic sea, submitted to

westerly almost the year long. The arid area agrees

well with paleodata. Indeed, dry-adapted ¯ora was

largely present over Baltica from west (England) to

east (Russia) except over the northern margin along

the Arctic Sea. We make the hypothesis that this

simulated arid area in the Pangea B experiment has

reached its maximum extent. A higher range in a

Pangea B would only dry more the arid areas and

leave unchanged the northern points, submitted to

westerlies. If we compute the percentage of arid

area produced in the other scenarios with respect to

the maximum extent, we simulate only 25% of arid

area (located along the Zechstein Sea) in a Pangea A

without any relief with respect to the maximum arid

extent. The percentage of arid area increases

obviously with an increase in elevation. We suggest

that a good agreement between paleodata and simu-

lated climate is found close to the lower limit (annual

mean precipitation equal to 0.33 mm/day) of the Fig.

15e. It implies a mean elevation of some 2000 m in a

Pangea B and about 3000 m in a Pangea A.

The Variscan elevations, which are required to

reconcile climate modelling and paleodata can be

compared with different geodynamic contexts. In a

Pangea A type reconstruction, a high relief is


required over southern Europe to induce an aridi®-

cation of Baltica and southwestern Laurussia.

However, an open ocean is located immediately

southward of the remnant Variscan orogeny. As

pointed out by (Matte (1986)), this geodynamic

context does not involve a continent±continent

collision that could create an important shortening.

A high relief of Andean type created by plate

subduction under the south of Eurasia [see for

example (Molnar and Lyon-Caen, 1988)] would,

however, be a possible mechanism. Such a subduc-

tion exists along the southern margin of Eurasia:

the closure of the Paleotethys Ocean involves

northward plate motion with an average velocity

of 13 cm/year between the Permian and the ®nal

collision of Iran with Eurasia by the middle/late

Triassic (Besse et al., 1998). However, a compila-

tion of subduction related volcanism shows that a

subducting plate cannot be found in the interesting

region, but only far more to the east, close to the

Caspian sea (Kazmin et al., 1986). An Andean type

mountain belt due to a subducting plate therefore

appears unlike.

Another possibility is that these mountains issued

from the Variscan orogeny remained high a longer

time than previously thought. According to Becq-

Giraudon and Van Den Driessche (1996), the maxi-

mum elevation (5000 m) is reached during the Stepha-

nian (300 Ma), which is also the youngest age limit of

granites and metamorphism corresponding to the end

of major shortening phases in these regions (Matte,

1986). Becq-Giraudon and Van Den Driessche (1996)

and MeÂnard and Molnar (1988) propose a rapid

collapse of the range during the Late Stephanian and

the Autunian (Early Permian). The absence (or low

thickness) of clastic sediments in southern Europe


0

0.5

1

1.5

2

2.5

3

3.5

0 1000 2000 3000 4000

Mea

nan

nual

prec

ipita

tion

(mm

/day

)

Elevation (m)

PangeaA

Pangea B

Trop

ical

hum

idar

id

Fig. 15. Estimation of the Variscan mountain elevation based on a model±data comparison. Triangles represent the annual mean precipitation

(mm/day) averaged over Baltica (only land points) in function of the elevation of the Variscan/south Baltica range (m) for different experi-

ments. The solid line links points from these two clusters. We then extrapolate each curve from low to high Variscan elevations using an

exponential function (dotted line) because this function remains positive as the precipitation also does, and offers the best correlation coef®cient

(above 0.99). The thin line accounts for the variability of the signal. We also report the criteria of aridity de®ned by Walter (1984) on this ®gure

(dashed lines). Two cases have to be considered. An arid climate receives no more than 1.33 mm/day during at most 3 months. Thus, as soon as

the mean annual precipitation exceeds 0.33 mm/day (3 months £ 1.33 mm/day/12 months), the climate possibly evolves from arid to semi-

humid, and is thus the lower limit. The upper limit is de®ned by an annual precipitation rate of 1.1 mm/day, which corresponds to 10 months

with barely more than 1.33 mm/day and 2 months without any precipitation (1.33 mm/day £ 10 months/12 months). This is the lower limit of

the tropical humid climate.

younger than Autunian is interpreted by these

authors as an evidence of complete summits erosion.

The altitude of 500 m proposed by these authors is

unable to reconcile the simulated climate and paleo-

data. For our simulations to be in agreement with

paleodata in a Pangea A con®guration, we must

prescribe a 3000 m high range. Thus, the Variscan

range would have decreased by only 2000 m in

about 50 millions years. This very weak collapse is

unlikely.

On the contrary, a Pangea B implies a collision

context between Gondwana and Laurussia. Moreover,

the active dextral strike±slip fault at the boundary

between the two landmasses may easily account for

a range less than 2000 m high responsible for the dry

climate over the whole Baltica. Finally, the last

constraint on the elevation is provided by the migra-

tion of Zechstein ¯ora. This ¯ora assemblage is

observed in the Lybian basin of Permian age. The

presence of an elevated Variscan range at the

Permo-Carboniferous boundary may imply that the

migration of Zechstein ¯oral from Baltica to Gond-

wana occurred before the growing of the range.

Indeed, the high altitude of Variscan range necessary

to reconcile paleodata and simulated climate in the

case of a Pangea A would constitute an impassable

barrier.

6. Conclusions

A set of sensitivity experiments has been

performed with the aim to investigate the climatic

impacts of the Pangea con®gurations and mountain

elevations. The peculiar con®guration of Pangea

generates three main climatic zones: (1) A warm

temperate climate accompanied by seasonal precipi-

tation characterising a monsoon circulation over the

eastern side of Gondwana. (2) A cold temperate

climate marked by strong annual thermal amplitude

at high latitudes in Gondwana and in Siberia. (3) An

arid belt in the subtropics over the western side of

Gondwana and Laurussia.

Between these three broad climatic belts in Pangea,

two relatively thin buffer zones are found. Between

the high latitudes and the subtropics, a warm to cool

temperate climate is simulated. This climatic belt is

directly linked to the location of precipitation induced

by storm tracks along the mid-latitude jet-stream axis.

Between the arid belts at low latitudes, the climate

remains warm and nevertheless experiences signi®-

cant precipitation, the location and the intensity of

this rainfall being dependent of the orography. At a

large scale, this description remains valid for both

investigated Pangean con®gurations. However, the

latitudinal shift between Pangea A and B induces

regional temperature changes because of differences

in incoming solar radiation. It also leads to precipita-

tion changes over Gondwana. Despite these differ-

ences, the simulated climates for each con®guration

are relatively similar. Comparisons between simu-

lated climates and paleodata show a good agreement

in all areas except at low latitudes. Based only on the

paleoclimatic differences in Gondwana due to

Pangean con®guration, we are not able to propose

one con®guration rather than another. The use of

sensitivity experiments is an interesting way to inves-

tigate and better constrain the paleogeographic recon-

structions. The ®nal interpretation is, however,

dependent on available paleodata. The elevation of

mountain ranges appears to be of capital importance.

The impact of the Appalachians and ªVariscanº fold

belt altitudes at low latitudes of Laurussia and Baltica

are a more important forcing factor than the Pangean

con®guration itself. The comparison between the

simulated and observed climates implies an elevated

Appalachians fold belt with a mean elevation of

4500 m, similar to the modern Himalayas. This high

range modi®es deeply the atmospheric circulation and

thus the climate. The strengthening of moisture advec-

tion toward the ¯anks of the range and the deeper low-

pressure cell along its foothill lead to a drying of the

adjacent plains. However, the changes in elevation of

the Appalachian fold felt in¯uences only the adjacent

areas.

Whatever a A or B Pangea con®guration, a range

in the south of Europe is required to reconcile simu-

lated climate and paleodata indicating an arid climate

over Baltica: this range de¯ects the seasonal moisture

¯ow blowing from the Tethys and avoids its penetra-

tion further inland. The existence of such a range

implies a tectonic mechanism to induce or at least

to sustain high altitudes. In the case of a Pangea A,

no northward moving plate may account for a range

of Andean type. The age of major erosion basins

indicates that summits have been eroded at least


20 Ma before our reconstruction. On the contrary, the

collision context and the dextral strike±slip fault at

the Gondwana±Laurussia boundary in a Pangea B

context may easily account for a 2000 m-altitude

range necessary for generating the dry climate over

Baltica. The ®nal result of this study is, therefore,

that even if we are not providing any direct constrain

on Pangea con®guration, we do show that Variscan

elevation has to be around at least 2000 m to account

for Baltica climate, and this elevation is more realistic

with Pangea B, which is an indirect constrain on paleo-

geography con®guration.

Acknowledgements

This work is supported by the French scienti®c

program Dynamique et Transfert Terrestre, INSU.

This work was carried out using the IDRIS and

CEA computing facilities. We thank J.Y. Peterschmitt

for providing the postprocessing package. We also

thank Masa Kageyama and Stuart Gilder for improv-

ing English. Reviewers A. Ziegler and J. Parrish are

acknowledged for their critical evaluations of the

manuscript. This is an IPGP contribution 1690,

LSCE contribution 0406.

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