The Permo-Triassic of Southern Tunisia — biostratigraphy and palaeoenvironment

The Permo-Triassic of Southern Tunisia — biostratigraphy and palaeoenvironment

Review of Palaeobotany and Palynology, 66 (1990): 273-291 273 Elsevier Science Publishers B.V., Amsterdam The Permo-Triassic of Southern T u n i s ...

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Review of Palaeobotany and Palynology, 66 (1990): 273-291

273

Elsevier Science Publishers B.V., Amsterdam

The Permo-Triassic of Southern T u n i s i a - Biostratigraphy and palaeoenvironment F a t m a K i l a n i - M a z r a o u i 1, S a l o u a R a z g a l l a h - G a r g o u r i 2 a n d B e y a M a n n a i - T a y e c h 3

1ETAP, 27 Bis, Avenue Khereddine Pacha, Tunis, Tunisia 2Facultb des Sciences, Dbpartement de Gbologie, Laboratoire de Micropaleontologie - - Campus Universitaire, Tunis, Tunisia 3INRST, Borj Cedria, Hammam-Lif, Tunis, Tunisia (Received January 5, 1989; revised and accepted March l, 1990)

ABSTRACT Kilani-Mazraoui, F., Razgallah-Gargouri, S. and Mannai-Tayech, B., 1990. The Permo-Triassic of Southern Tunisia - Biostratigraphy and palaeoenvironment. Rev. Palaeobot. Palynol., 66: 273-291. The ages given to the Permo-Triassic sedimentary strata of Southern Tunisia often prove to be inaccurate. The Upper Permian of Southern Tunisia, the only marine outcrop known in Africa, is characterized by four sedimentary sequences: (a) a basal unit represented by sandy shaly deposits with marine fauna; (b) a unit of carbonate sediments; (c) a shaly unit; and (d) an uppermost unit represented by sandy shaly deposits. This present study is mainly based on data from two wells drilled in the area to the south of the outcrop sections. Combined palynological and micropaleontological evidence allow the recognition of the Permo-Triassic boundary, the proposal of a biostratigraphic model of the different Triassic units and the reconstruction of the palaeoenvironmental history. The main results of this study are as follows: (a) The Upper Permian without microfauna has been dated by the presence of characteristic palynomorphs such as

Lueckisporites virkkiae. (b) An important disconformity (stratigraphic uncomformity) has been demonstrated at the Early Scythian level;it is marked by the absence of part of both the Upper Permian and Lower Scythian. This phenomenon seems to be widespread. It has been reported in the Middle East, in Libya and has been found for the first time in Tunisia. (c) The Upper Scythian is characterized by carbonate sediments containing a marine fauna (Meandrospira pusilla) and the annelide (Spirorbis phlyctaena). The palynoflora contains Endosporites papillatus and Alisporties grauvogelii. (d) The Anisian-Carniandeposits consist of clastic sediments indicating an important continental input into the area. Although the faunas are absent, the palynoflora contains representatives of both the Alisporites and Densoisporites groups which indicate a lagoonal to Sebkha environment. From the north to the south, the sedimentation varies laterally in both lithology and thickness; in the north, the sediments are calcareous while in the south they are siliciclastic.

Introduction F o r a long time, several a u t h o r s (e.g., Glinzboeckel a n d R a b a t r , 1964; Busson, 1967, C h a o u a chi, 1985; Bou Aziz, 1986) have been involved in the study o f the Permo-Traissic o f s o u t h e r n Tunisia. I n spite o f their detailed investigations, the stratigraphy o f the region r e m a i n e d p o o r l y k n o w n . The present study based o n a j o i n t palynological

a n d m i c r o p a l e o n t o l o g i c a l investigation h a d the following three m a j o r objectives: (1) T o accurately determine the Permo-Triassic boundary. (2) T o reconstruct the Permo-Triassic e n v i r o n m e n t s of deposition. (3) T o establish a reliable c o r r e l a t i o n between the studied wells in the s o u t h o f T u n i s i a a n d Libya. The samples were collected f r o m two wells a n d one

274

F

field section, all of them located in the south of Tunisia.

The Upper Permian

Description Several exploration and development wells have penetrated the Upper Permian in the south of Tunisia; the only outcrop known in North Africa is that of Jebel Tebaga located in the south of the country (Fig.l). This outcrop shows a facies dominated by a succession of sands, clay laminated bioclastic limestones and bioherms with calcisponges and algae. This faunal rich section which contains Yabeina syrtalis, Dunbarula mathieui has not yielded palynomorphs. The palynofacies, however, indicates the presence of ligneous material. In the Kirchaou-1 (KR-1) well (Table I), the Upper Permian is subdivided into five lithological units (Kilani, 1986), classified as follows:

.....

I

GOLFE DE GAOES

)

~ ~

I

..........

ffi G._I_L O C A T I O N • outcrop section "1~ Exp[orotion wells

/

LG)}~" ~J

MAP

i ÷ \x

~ale

:

I/I~ 000

AL

Unit l Thickness: 206 metres Facies: Predominantly dolomites at the base and alternations of sands and shales at the top. Fauna: Very rich with: Pseudoschwagerina, Rugofusulina, Quasifusulina, Paleotextularia, Globivalvulina, Ammodiscus; associated with algae (Dasyclads) and remains of echinoids, brachiopods and gasteropods. The fusilinid assemblage therefore indicated a Late Carboniferous to Early Permian age. We have observed Quasifusulina and Dvinella, a pseudoalgae, which generally disappears in the Upper Carboniferous, but which is locally known in the lowermost Permian, i.e. Asselian (D. Vachard; pets. commun.). Palynoflora: Very diversified, with Taeniaesporites novimundi, Chordasporites sp., Sulcatisporites ovatus, Cycadopites rarus, Klausipollenites schaubergeri, Lueckisporites virkkiae, Microcachryidites fastidioides, Platysaccus radialis, Platysaccus cf. papillatus.

-:o. Medenme

I

E1

KILANI-MAZRAOUI

\

I

\ ~v-

\
PERMO-TRIASSIC OF SOUTHERN TUNISIA TABLE I m

P

S t r a t i g r a p h i c a l d i s t r i b u t i o n : KR.1

A

L

Y

N

0

M

0

R

P

14.1

~,~ ~,

~

o~ ~

~.~.

.~

,~.~ .~ ,~ ~,-~" . ~.~.~,.



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,e

-~

*e"

100. :':'. :" "

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y

vii

200 ~ ..-:-rT-~;

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o•

o J• oB o •

oo •

O•OO•

8 ~ o g o o g o

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8 0 0 - ~

v

1100 IV

~

22U-

)) ,~m

m

O Od

I

X' 2155

COt~.

SHALLOW MARINE TO

SHALLOW MARINE

IL

ILl

MARlNE

TO

LAGOONAL TO CONZ "~

X

CONTINENTAL

a

• ll



e

I

i LXGOO~AL I

70

MARINE

ll

~

• ,

@

oe

~l)



~ARINE





o

COkr'f.

ENVIRONMENT

Ga~t~opode~

>.

Z

c

8~dybla Dip~ pke~a SpOw~b~ pl~tc~en~ Pe~z~ca~cu~u~ A~j-e~ Ec/~b~de~u.e~ 8~uzch~pode~

"-rl 3>

Ovine~a

0

30

o

"D

30

o

Tub.ec,L~no. Po.teotex~tu.t.~t.~t

G~ocodLum Gy~opo~eJ~a ~ o ~ d i.op6~

Gto~,~p~

Gto~v~vut~mx g~e~

Nodo6~e O~code~

t~m~6pJJ~ p u ~

Oe~o~poc~t~ .ejba.~gi~.

~t.~dopodoca~p~e~ S~tcct~po~Lte~ ova,tu~

P/,n~g~aceu.~ c~. pc.pi.U.ctaz,

~uwcack~.~te~ do~CMXo~de~ P/.aCy~accu~

T~e~J~e4po.~ e ~ ~oviauJeRt,~ Cycadopi~e~ ttatu~ ~p~e~,Xe~ ,~chaube~ge~J. Luec/~,~tpo,~.~e~ v ~ . k ~ e

Taes.~e~po~.~e~ Ap

T~e~ti.~e,~poa~,~.e.~novimundi L e ~ e ~ e ~ ~p

t/~h¢ck.~n, ~eguZa~ae

oo

~0

279

PERMO-TRIASSIC OF SOUTHERN TUNISIA

This palynoflora indicates a Late Permian, and probably Murghabian, age.

-Unit II Thickness: 545 metres Facies: carbonate deposits. Fauna: Represented by Ophtalmiidae, Hemigordius Ammodiscidae, Globivalvulina, Glomospira and rare fusulinids associated with algae (Mizzia velebitina, Gymnocodium) and some ostracods. Palynoflora: absent. -Unit III Thickness: 224 metres Facies: Dominance of limestone with intercalations of anhydrites. Fauna: Absent. Palynoflora: Restricted to Taeniaesporites noviaulensis. -Unit IV Thickness: 85 metres Facies: Marl and dominant limestone Fauna: Consists dominantly of Globivalvulina greca, Calciternella associated with algae (Permocalculus, Mizzia) and remains of bivalves, gasteropods and echinoids. -Unit V Thickness: 425 metres Facies: sandy Fauna: Absent Palynoflora: Lundbladispora brevicula, Lueckisporites sp. A dominance of ligneous material is observed throughout the succession from unit I to unit V (Fig.2). Eastward at the Kasbah Leguine-3 (LG-3) well location, the Upper Permian is divisible into two units (Table II): -Unit 1 Thickness: 135 metres Facies: Interbeds of anhydritic and carbonate sediments grading to limestone and dolomite occur throughout the unit. Fauna: Dominantly echinoids and Ophtalmiidae associated with ostracods. Palynoflora: Tympanicysta stoschiana.

-Unit II Thickness: 237 metres Facies: Sands and limestone at the base grading to shale at the top. Fauna: Composed ofAmmodiscidae, Endothyridae associated with debris of bivalves and crinoids. Palynoflora: Palynomorph assemblages diverse but dominated by: Lueckisporites singhii, Veryhachium and Tympanicysta stoschiana. Palynofacies: Shows dominant ligneous debris (Fig.3) The occurrence of Punctatisporites minutus, Cycadopites rarus, Lueckisporites virkkiae in well KR-1, and Lueckisporites singhii in well LG-3 allowed us for the first time to give a Late Permian age to units I-V and I-II respectively in these two wells. Environment of deposition During the Late Permian times, the south of Tunisia was characterized by a dominance of carbonate deposits. A marine fauna composed of benthic foraminifera associated with green algae, indicating a shallow marine environment, has been recognised. In well KR-1 (Table lII) there is evidence of mixed sedimentation grading from evaporites to open marine with some fluctuations before reaching a complete continental environment. At the LG-3 well location to the south west, the succession is different from that mentioned at KR-1, being essentially a mixed sedimentation grading to open marine. (Table IV) Towards the east (Libya), sedimentation grades progressively from subcontinental to high saline without reaching marine degree (Adloff et al., 1986). The Triassic

Triassic outcrops are well represented in the south-eastern part of Tunisia, and extend into Libya. The first studies, in that part of the country, recognised the classic subdivisions of the Germanic Triassic (RAUCHER, 1974-1978): (a) a detritic, continental lower unit, (b) a calcareous, marine middle unit and (c) an evaporitic, lagoonal upper unit. Due to the absence of fauna and palynoflora, the

391.6_393.2 m

I S4.3_fSS,gm

494,8_499.8m

1015.3_1016.7m

915_915.8m

736.8_ 738,4 m

664,4_665.5m

601,5_602.5m

Fig.2. Palynofacies evaluation of the well KR 1.

260.3_262m

492.8_494.8m

367_368m

105.3_107m

225 m

325m

55,3_56.7m

[email protected]_ @ Q G @ Q @ (Y Q @ @ Q Q @ 1336,4_1338 m

122~.6_1231,3m

114 2 _ I 149m

1135.6_1137m

1053.8.1054.8m

Q Q @ @ @ 1730.4_173Zm

1595_1596m

1523.1 _1524.6 m

1465_l/~Trn

1435_1438rn

2165 m

2137.75m

Q

2007.25m

1961_1962m

194l$_ 1949 m

@ Q Q O G @ Q @ ~

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AcriJta rchs

Polten & spores

Cutictes

Amorphous organicmatter

Coal

0

> N

z

F

PERMO-TRIASSIC

OF

SOUTHERN

281

TUNISIA

TABLE II

Stratigraphical distribution: LG.3 ICROAUNA

PALYNOMORPHS

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N 00

0

e

.%.....

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t

oe

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1129~,9

,-.

scale

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Permo-Triassic boundary was impossible to determine in the outcrop section. At present the Triassic succession is better documented in the well sections in the region. Four lithological units are recognised: (a) a lower unit dated as Scythian, (b) a middle unit dated as Anisian-Carnian and (c) two upper units belonging to the "Muschelkalk" and "keuper" facies. A marked lateral change of facies effects these Triassic deposits in a north-west to south-east direction across the region.

Upper Scythian Description In well KR-1, from base to top, the lithology changes from grey-brown shales with thin beds of slightly dolomitic, detritic limestone containing phosphatic remains, overlain by shaly dolomitic sediments to a shaly, sandy deposit at the top (Table I, III). Laterally, towards the south east (LG-3) an increase of detritic sediments is noted (Table lI, IV). The microflora is rich and

396 m_t,00m

500 m - 505 m

550m_SS5 m

210m- 216m

300m_305m

Fig.3. Palynofacies evaluation of the well LG.3.

L,05m_/~10m

155 m_ 160 m

@ G @ G Q

130m_1/.0m

875m_880m

955m_960m 755m_760m

835m_ 850 m

695 m -700 m

655 m_660m

805m_810m

G Q @ Q Q

595m-ro00m

@ @ @ @

<]

.~

Acritarchs

Pollens & spores

Cuticles

Amorphous organic

Coal

1129.9m - 11/.,L,m

O Q I025m _ I030m

matter

283

PERMO-TRIASSIC OF SOUTHERN TUNISIA

TABLE IlI E n v i r o n m e n t o f deposition: K R . l

,m'--V C~

MICAOAUFIA

._..I

PALYNOMORPMS

['FtVIROMMCMT

HARINE CONTINENTAL ,p: ,.:.'o

I 00.

.>

200.

;.,__.-' ~ ~:~ ~ ~.

.

225325_ 367-368 391,6-93~L

~:"

Alisporites

~ "--"-- -^ " ^ ,,, ^

,.,~ = z £E t~ uJ<~

O - - O.. P, ,.jn. >-'~_

nuthallensis

: .....

492.8 -

/_!

494.B 494.8-

"

Meandrospira pusilla Spirorbls phlyclaena

"

' ' 499.8 "_' :601.5-¢~2,5. - - - 6

9

5

"

Veryhach i u m r e d u c t u m Yeryhachium t rispinosum A p i c u l a t isporites d e c o r us Endosperites p a p i l l a t u s Psilatriletes t riasslcus Veryhachium irregularae Micrhyst ¢idi um sp. Taenlaespor~tes sp. Ret usot r iletes mesozoicus

~

7158,00

:'.'."-'"

Lund b l a d i s p o r i t e s b r e v i c u l a Taen i a e s p o r ires n o v i m u n d i Le i o t r i l e t e s sp.

• .-:': r:- '

.,...:,. ,.

Z

Z :,

3[:

-

-. ---,,

:_

1 1 0 0 . : ~ ' . -~-, ,. / . '

1231,3

l

J

Globivalvulina greca P e r m o c a l c u i us Mizzia

LJJ ill

n

",, ~ . . . .

n

C..,?.7 , , i I

n..

I

|

, , , ;'! " iw" n

re"

.

.

.

Mem~gora~us

'

Tubiritino

' ILl

LIJ

O.

"IF

,

Paleotextularia

I i

-.--. I

O.

J I!

•- i

-,

tL

~

; - L, 1985

~

.

.

.

.

.

1995

.

Geinitzina Glomospira v.mnoco.,um ... _.Cyr°E°rella H e m Jgordiopsis

.

~ .~ _/ ,_/ •• " / --"/ . I

1

BradLjina Diplospherina Algues Echinodermes Brochiopodes

Gosteropocle$

Lueckisporites sp. T a e n i a e s p o r l t e s novktulensis Cycadopites r a r u s Kl~pellenites schaubergeri Lueckisporltes v;r kkiae NicrocQchryid/tes fastidloides P l u t y s a c c u s r a d ial;. s R a t y s a c c u s cf. p a p i l l a t u s Punctato,cporites cf. m ; n u t u s S i r iadopodocaKplte$ r a r u s S u l c a 4 i s p o r ;tes ova~us

284

F. K I L A N I - M A Z R A O U I ET AL.

TABLE

IV

Environment

of

LG,3

deposition:

MI(ROrAUNA PALYMOMOP,PNS

....J

-r-p-..

-- i

v

MARINE

CONTINENTAL

3 ~,'Z:':";',:., ... / . . . / i

-f..-ft. 14515CI " " : 155-1 fw~,. :..::..'.:.., 1 6 5 4 70 . .' , , ' .

u~ Z L~< (~Z

210~15" • . . . . . ~2

flint' --

7

Z

< I112

--r

nr

£1. _J

7 <

Dupliclsporites cf 9ranulatus Microcachryidit es fast idioides Raracirculina scurriiis Pityosporites n e o m u n d a n u S Pret ricolpipo LLenltes bharadv~jii ACcinct ispor Hes l i g n Q t u s 295"400, "=. ~ Alisporites tor(zl~s .. TT:.. Angustisulcites grondis Duplicisporites granulat us r " Psilatr iletes t r i(lssicus Orotohaploxypin us sarnoilovichii Simeonospota khlonavoe I i.: "l Sulcctisporites krausel i 59~600' ' Sulcollsporites sp- C . Sulcosacclspora rn inuta Tr iadispona staplini . i r Yerrucoslsporites cf contactus • Verr u¢osispo¢ites pseudon~ nulae _". ~: Meanerospim pusilla Verrucosi.%oor[tes remyanus ,~._2~J ,Microcachry dtes doubLngeri Labi isporites g r a n u l Q t u s ~'Z'5-850r- . . . .

Z <

~85-890"

i

Z u.I l:k

I

--, -- - ' ,

"17" 955-960 Q_

Lueckispmites singhii Veryhachium reductum

r

Nodosoriidoe

~80-985.--.~--r:-,

Ostrocodes

i 1129,9.

-- "-~ j

diversified especially at the top. The following species are recorded: Endosporites papillatus, Densoisporites nejburgii, Densoisporites sp., Psilatriletes triassicus, Apiculatisporites sp., Retusotriletes

mesozoieus, Calamaspora tener, Taeniaesporites sp., Veryhachium, Micrihystridium, Alisporites grauvogelii, Cyclotriletes granulatus, Voltziaecaesporites heteromorpha, Alisporites parvus, Deltoispora helieoidalis, Alisporites cireulicorpis, Labiisporites granulatus, Microcachryidites doubingeri.

While the microfauna is rare, the main taxa recorded are: Cyclogyra, Ammodiscus, reophax,

Ammovertella, Happlophragmoides, Meandrospira pusilla, associated with the annelide Spirorbis phlyctaena. The occurrence o f Endosporites papillatus, Densoisporites nejburgii and Alisporites grauvogelii indicates a Late Scythian age. The palynofacies analysis s h o w s a d o m i n a n c e o f ligneous material (Figs.2,3). The species Meandro-

PERMO-TRIASSIC

OF SOUTHERN

285

TUNISIA

TABLE V

Environment of deposition: K 1-23

,n ,

PALYtlOMOIPtllS EMVIROMI'I[MT

MICP, O AUflA

.,.,==1 ",L'-"

MARINE CONTINENTAL

,,::x:

z

--


~

P-

Z .. <~

~l ,_ N

-...--~.: : . ":.'.. .--: ,_.,.

U

<~

"'~'. ...-..:.:.~ .. -:.:...:

r~ hl 0. D

-~--:~ •.~.l-...... ,-:.--,-

R a s -'----,= Hamia -=-- -

Triadispora Triadispora Triadispora

falcata aurea s~t.opl in i

i.°. ,',. . i . ....'.~. __

IFI ~.

.'" :.:,

Z ,~

:.:.:.'.. :.'.'"

.~ ." ".-.-. ~u v . ' . ' . . . n

Hexasacciles Endosporiles

un

~

,~' ,.'.

Yoltziaceaesporites

--

.~ " " :. "' OJ | . .. .. '...... . 1

Oc

ILl ..j

i

.d:3,

--

t-

I

-" :-', :.'.J • - ".".", "." . ' - , •

z

c~ ~

hetero-

morpha

"::'i i.! .".'. ",

r~

,""

muelleri papillatus

..

• :.~':'" ,:/.:..:(:'i -

--

:E

"'-'.'.':: -..,.:.:.. , :." - ",.,..

r..'~ U.i v '

j ~

r,-Z U.I
o-i-n, : : : ) ~ ~ ~

--

-.":-'d, Y~ ".: ." .'."

~ :~':'.'~ " ~ ~ ":'.~.':'.:." ~ ",'.'..: - M e a n d r o s p i r a U0~la

Yeryhmchium Micrhystridium

_ pAu. s i l l a

irregularae sp.

C~lamospora ~ener Spores ind~termine'es . ~ E. n d .o s p.o r j .t . c s P a D i l J q t l ~ i _ _ Lueckisporiles

v~rkkiae

286

spira pusilla is characteristic of Late Scythian deposits still called Campilian in the western Carpathians where it had been recognised as a zonal fossil (Salaj, 1969). Therefore its occurrence in the studied level further confirms the Late Scythian age.

Environment of deposition The Tethyian sea transgressed over the Upper Permian shales and sands, covering all of southern Tunisia. As a result of that transgression, carbonate sediments containing benthic fauna (Ammodisidae, Meandrospira associated to Veryhachium, Micrihystridium) are deposited. This marine phase, which is well developed in well KR-I, is reduced towards the east well LG-3 where the Scythian carbonate deposits are reduced to a dolomitic bed containing Meandrospira pusilla. These foraminifera are very small and represent a dwarf population. This phenomenon is probably due to an environmental variation. Indeed Adloff et al. (1985) explained that this species during the Triassic underwent: "le nanisme tagunaire et joue le r61e d'esp6ce pionni+re pour des milieux non encore occup6s par les foraminif+res au cour de leur histoire".

Anisian-Carnian Description In the KR-1 well, the facies at the base of the Anisian sequence is mainly composed of shaly, sandy and anhydritic alternations grading at the top into a hard compact sandy dolomite (Table I, III). In well LG-3 to the east, the Scythian facies persists into the Anisian with the same shaly sandy alternations (Table II, IV). The palynoflora is composed essentially by Triadisporafalcata, Triadispora forme Y, Triadispora epigona, associated with Alisporites circulicorpis, Chordasporites singhii, Hexasaccites mulleri and Verrucosisporites remyanus. Fauna is absent. The palynomorph species described in the Anisian of the Tripolitanian Triassic (Adloff et al., 1986) as well as other parts of the world, e.g. Germany (Klaus, 1964) and France (Adloff and Doubinger, 1969), were also found in Tunisia. However, in well LG-3 the palynofloral association

F. K I L A N I - M A Z R A O U I ET AL.

is different from the one found in KR-I; it is represented by the following species: Verrucosi-

sporites pseudomorulae, Psilatriletes triassicus, Leiotriletes sp., Triadispora staplinii, Sulcosaccispora minuta, Sulcatisporites sp.C, Sulcatisporites kraeuselii, Klausipollenites schaubergeri, Angustisulcites grandis, Alisporites toralis, Pityosporites neomundanus, Paracirculina scurrilis. The presence of Triadispora falcata, Sulcosaccispora minuta and Paracirculina scurrilis allows the allocation of an Anisian-Carnian age to this sequence. Due to the absence of biostatigraphic markers, the Middle Triassic-Upper Triassic boundary remains ill-defined. The palynofacies analysis shows a dominance of ligneous material. Unstructured organic matter is more significant at the base of the sequence, whereas cuticule-remains are important at the top (Figs.2,3).

Environment of deposition In well KR-1 (Table III), the mixed sediments containing bisaccates (Alisporites) indicate a lagoonal environment (sebkha type). To the southeast in well LG-3 (Table IV), the Anisian-Carnian becomes rich in detritic sediments suggesting an environment extending over fluviatile plain. Further to the east, in northwestern Libya (well K1-23; Table I; for location of well see Adloff et al., 1985), the marine influences during the Anisian were almost insignificant with a total absence of any microfauna. During this time (Anisian) we have probably a low coastal plain temporarily invaded by the sea. During the Ladinian, the depositional environment corresponds to a near shore regime, grading during the Carnian into a more arid environment confirmed by the presence within the sequence of representatives of the Circumpolles. It is to be noted that the same landscape prevailing at the end of Scythian (shallow platform with tides and lagoons) continued during Anisian-Carnian time. Detritic microfaunal material is present but marine influences are missing.

The "Muschelkalk" Description Determined at well LG-3 (Table II) only, the "Muschelkalk" facies is predominantly dolomitic,

287

PERMO-TRIASSlC OF SOUTHERN TUNISIA

During the time of "Keuper" deposition, the south of Tunisia was covered by anhydritic sediments, without microfauna and palynoflora, indicating a lagoonal environment, with intensive evaporation (Table IV).

contains a carbonaceous facies with marine fauna, not observed in Tunisia. It is therefore presumed that the LG-3 well location corresponds to a palaeo-high which rapidly evolved into a lagoonal environment with Meandrospira pusilla. Conversely, at the KR-1 well (Tunisia) and K1-23 well (Libya) locations, the transgression was major, but the Late Scythian sedimentation shows evidence of a regressive phase at well KR-1 (Table III). During the Middle Triassic, the same arrangement of facies occurred in both Libya and Tunisia with a dominance of anhydritic sands and shales indicating a location on a wide platform with evaporites and silt deposits. At the same time, we note the occurrence of the same faunal and floral associations and the same unconformity in both Libya and Tunisia. The marine influences are important in the south-east of the country and in Libya. It is therefore suggested that two separate provinces existed, a carbonaceous one to the north and a transitional one to the south.

Correlation with Libya

Conclusions

A correlation study of the Permo-Triassic of the south of Tunisia with western Libya is presented in Figs.4-6. During the Permian, one can note lateral facies and thickness variations of the sequence from the north-west to the south-east (Figs.4,5). In the north-west, the facies is essentially calcareous, related to a shallow marine environment. In the south-east the material is rather sandy indicating a subcontinental environment. The sequence is thicker towards the north-west of the area which may represent the deeper part of the marine basin with maximum subsidence whilst a platform facies with detritic sediments exists in the south-east of the area. Also during the Triassic one may observe variations. In the south of Tunisia at KR-1 well the lower Triassic is calcareous grading to sandy deposits at LG-3 well location. In Libya the Tethyian sea invaded all the Libyan craton. To the north, especially in Sicily (Fig.6) the Upper Triassic

From the palynological and micropaleontological data, mentioned above, the following conclusions can be made: (1) The occurrence of Lueckisporites virkkiae, Lueckisporites singhii (palynomorphs), Meandrospirapusilla (benthic foraminifera) allows the recognition of the Permo-Triassic biostratigraphic boundary. (2) The Upper Scythian-Anisian boundary is well defined. However, the Middle Triassic-Upper Triassic boundary remains in doubt due to the absence of diagnostic biostratigraphic markers. (3) A stratigraphical gap was established for the first time at the Early Scythian level in Tunisia. A similar phenomenon has been reported from the Middle East and Libya (Adloff et al., 1986). (4) The sedimentological data for the PermoTriassic boundary remain insufficient to resolve the paleogeographical evolution during this period. (5) The Upper Permian corresponds to a wide shallow water sea platform. (6) The Lower Triassic corresponds with shallow

occasionally sandy. Palynofloras are absent, the fauna is rare and represented by debris of echinoids and ostracods only.

Environment of deposition During the deposition of the "Muschelkalk", the sea returned with calcareous deposition including fossiliferous glauconitic dolomites specially at the base of the sequence (Table IV).

The "Keuper" Description Composed of shaly, anhydritic alternations, faunal remains and palyofloras are missing (Table II).

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marine calcareous sedimentation that invaded both the south of Tunisia and Libya. This proves the extension of a marine transgression. (7) During the Middle Triassic a detritic sedimentation with occasionally marine carbonate material took place with lagoonal deposits occurring towards the south-east. (8) During the Late Triassic, evaporites were deposited in southern Tunisia.

Acknowledgements We thank A. Kamel (ETAP, Tunis, Tunisia) D.Vachard (Institut Grologique Albert de Lapparent, Paris, France) HMISSI (Facult6 des Sciences de Tunis, Tunisie) for their contribution to critically read and correct the English text of the manuscript.

References Adloff, M.C., Doubinger, J., 1969. Etude palynologique dans le grrs fi I/oltzia (Trias infrrieur). Bull. Carte Grol. Alsace Lorraine, 22(2): 131-148. Adloff, M.C., Doubinger, J., Massa, D., Vachard, D., 1985. Trias de Tripolitaine (Libye): Nouvelles donnres biostratigra-

291 phiques et palynologiques. Rev. Inst. Fr. Pet., 40(6): 723-753. Adloff, M.C., Doubinger, J., Massa, D., Vachard, D., 1986. Trias de Tripolitaine (Libye): Nouvelles donn~es biostratigraphiques et palynologiques. Deuxirme Partie. Rev. Inst. Fr. Pet., 41(1): 27-72. Bou Aziz, S., 1986. La drformation dans la plateforme du Sud Tunisien (Dahar et Djeffara): approche multi et pluri disciplinaire. Thrse, Fac. Sci. Univ. Tunis, 179 pp. Busson, G., 1967. Le Mrsozo'ique, l/~re partie: l'extr~me Sud Tunisien. C.N.R.S., Paris, 194 pp. Chaouachi, C., 1985. Contribution fi l'&ude des palronvironnements et de la diagen~se carbonatre de la srrie permienne du Djebel Tebaga de Medenine (Sud Tunisien). Mem. D.E.A., Fac. Sci. Tunis, (Mimeograph.), 104 pp. Glintzboeckel, C. and Rabatr, J., 1964. Micraufaunes et Microfacirs du Permo-Carbonifrre du Sud Tunisien. BRILL, Leiden, 45 pp. Kilani, F., 1986. Etude palynologique et stratigraphique du Permo-Trias du Sud Tunisien. Mem. D.E.A. Fac. Sci. Tunis, (Mimeograph.), 117 pp. Klaus, W., 1964. Zur sporenstratigraphischen Einstufung yon gipsfiihrenden Schichten in Bohrungen. Erdoel-Z. 4: 119-132. Rauscher, R., 1974-1978. G~ologie de la Tunisie. l~re pattie: stratigraphie. Evolution paleogrographique de la Tunisie, centre Natl. Rech. Sci., Strasbourg (Mimeograph), 93 pp. Salaj, J., 1969. Quelques remarques sur les probl~mes microbiostratigraphiques du Trias. Notes Serv. G~ol., 31, Tray. Grol. Tunis.: 6-23.