Article
Reference
Triassic stratigraphic evolution of the Arabian-Greater India embayment of the Southern Tethys margin
HAUSER, M., et al.
Abstract
An exceptional, tectonically remarkably unaffected, nearly 200 m-thick continuous section of hemipelagic and turbiditic sediments, covering most of the Triassic is described from the Batain Complex of north-eastern Oman. According to conodont and radiolarian data the sequence spans the late Scythian to the early Norian, a time period of nearly 30 M. Coupled with a high resolution stratigraphy, the lithostratigraphy, sedimentology, as well as sequence and isotope stratigraphy of the section are documented. For the Triassic of the Batain Plain we propose the new name Sal Formation, which replaces the formerly used Matbat Formation, and subdivide it into three new members. The Sal Formation was deposited on the proximal continental margin of northeastern Arabia and records various depositional environments. The lower member is interpreted as the distal part of a homoclinal ramp which evolves to a distally steepened ramp during time of deposition of the middle member. The upper member displays a toe of slope position which is indicated by an increase of proximal turbidites. These sediments form part of a segment of the [...]
HAUSER, M., et al . Triassic stratigraphic evolution of the Arabian-Greater India embayment of the Southern Tethys margin. Eclogae Geologicae Helvetiae , 2001, vol. 94, no. 1, p. 29-62
Available at:
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0012-9402701/010029-34
$1.50 +0.20/0 Birkhäuser Verlag. Basel.
2001Eclogae
geol.Helv.
94 (200129-62
Triassic stratigraphie evolution of the Arabian-Greater India embayment of the southern Tethys margin
Marc Hauser,1 Rossana Martini.2 Steve Burns,1 Paulian Dumitrica,3 Leo Krystyn,4 Albert Matter,1 Tjerk Peters' & Louisette Zaninetti2
Key words: Stratigraphy. Sedimentology. Carbon isotope. Oxygen isotope. Triassic Batain Basin.Oman
ABS I
RAO ZUSAMMENFASSUNG
An exceptional, tectonically remarkably unaffected, nearly 200 m-thick con¬
tinuous section of hemipelagic and turbiditic sediments, covering most ofthe Triassic is described from the Batain Complex of north-eastern Oman. Ac¬
cording to conodont and radiolarian datathe sequence spans the lateScythian to Ihe early Norian. a time period of nearly 30 M. Coupled with a high resolu¬
tion stratigraphy, the lithostratigraphy. sedimentology. aswell assequence and isotope stratigraphy of the section aredocumented.
For IheTriassic of the Batain Plain we propose the new name Sal Forma- lion, which replaces ihe formerly used Matbat Formation, and subdivide it inlo three new members. The Sal Formation was deposited on the proximal conti¬
nental margin of northeastern Arabia and records various depositional envi¬
ronments. The lower member is interpreted as the distal part ofahonioclin.il ramp which evolves toa distally steepened ramp during time of depositionof Ihe middle member. The upper member displays atoe of slope position which
is indicated by an increase of proximal turbidites. These sedimenls form part ofasegment of the Neo-Tethyan embayment between Arabia andIndia.
The stratigraphie analysis indicates highly varying sedimentation rales from a minimum of 2 m/My around the Anisian/Ladinian boundary up to
15 m/My during Ihe Lower and Upper Triassic. Sequence-stratigraphically.the Sal sedioli is subdivided intosix third order cycleswhich are biochronological¬
ly well integrated into the global Triassic cycle chart. The mixed siliciclastic- calcareous upper member of the Sal Formation typically shows highstand re¬
lated carbonaie shedding. It is. therefore, an important test case forsequence- stratigraphic controlled carbonate export lo mixed basin fills. The well devel¬
oped sequence stratigraphie cycles are mirrored in the isotope patterns.
Additionally, the carbon and oxygen isotope data from the Sal Formation record the same chemostratigraphic markerat the Spathian/Anisian boundary known from other Tethyan sections.
Eine ungestörte, ca. 200 m mächtige Abfolge aus Turbiditen und hemipelagi¬
schen Sedimenten präsentierl einen grossen Teil der Triassedimente des Ba¬
lani Komplexesdes NE-Omans. Das Profil umfasst einen Zeitraum vonca.30 Millionen Jahren vom Oberen Scythian bis ins Untere Norian und ist mit sei¬
ner hoch aufgelösten Conodonten- und Radiolarienbiostratigraphie einzigartig fürden südlichen Tethysrand. Basierend auf Biostratigraphie. Lithostratigra¬
phie und Sedimentologie wurde das Profil mu Sequenz- und Isotopenstrati- graphie untersucht. Aulgrund der neuen Daten und Erkenntnisse definieren wirausschliesslich fur die Batain Region neu die Sal Formation mit ihrendrei Untereinheiten und ersetzen damit die in den Oman Mountains
definierte
Matbal Formation.Die Sedimente der Sal Formation wurden in verschiedenen proximalen Ablagerungsräumen m einem Meeresbecken der Neo-Tethys zwischen Arabi¬
en und Indien abgelagert. Diejenigen der Sal Formation, die am arabischen Kontinentalrand abgelagert wurden, zeigen zudem einen Wechsel derBecken¬
architektur voneiner distalen homoklinalen Rampe zu einersichvertiefenden Rampe und schliesslich zu einem Beckenabhang mit Turbiditsedimentation.
Im Typ-Profilzu sehen sind Meeresspiegelschwankungen und wechselndeSe¬
dimentationsraten der sudlichen Tethys. weiter der Zusammenhangzwischen Sequenz- und Isotopenstratigraphie. sowie ein deutlicher chemostratigraphi- scher Isotopenmarker für die Spathian/Anisian Grenze. Diese Erkenntnisse lassen sich mit Daten des nordlichen Tethysrandes vergleichen und mn globa¬
len Ereignissen in Zusammenhangbringen.
Introduction
The geology
of theBatain Plain
isdominated
byimbricated allochthonous units, consisting
offolded
andfaulted Permian
toLate Cretaceous marine sediments
andvolcanic rocks (Roger
et al. 1991:Béchennec
et al. 1992b;Wyns
et al.1992)
andfragments
ofophiolites from
theBatain Group (Immen¬
hauser
et al. 1998).This Batain nappe
stackmay reach
1.5-2 km in
thickness according
toBeauchamp
et al.(1995).
Because
of therelatively scattered outcrops
of thedifferent lithologies
andapparently chaotic structural situation, they were previously interpreted
as"Batain Melange" (Shackleton
et al. 1990). Based on
lithologie similarities between the Hawasina
Basin and theBatain Basin. Glennie
et al.(1974).
1 Corresponding author: Marc Hauser. Mincralogisch-petrographisches Institut und Geologisches Institut. Universität Bern. Baltzerstrasse 1. 3012 Bern.
Switzerland. E-mail hauser@mpi.unibe.ch
: Departement de Géologie et Paléontologie. Université de Genève. 13 rue des Maraîchers. 1211 Genève 4.Switzerland
1 Institut de Géologie et Paléontologie. BFSH2 UNIL.CH-1015 Lausanne. Switzerland
4 Institut für Paläontologie der Universität Wien. Althanstrasse 14. 1090 Wien.Austria
AdDaftah
IRAN 26' Shis
ArabianGull Oui/
oro"Wn Ra
salHadd
MII...11 2A-)
r\i
Sur 24911 Jaramah22' s
N^
SAUD ARABIA I I
2Ü 2480
\
; '-s
®
24 71)
52' 54' 56 58 60
Z /\w\ Bu Fashiuah //
/, MS AlKhabbah
24611
I
RuwaydahI.©
ArRuays2450 Musawa A Khaddah
®
SalÄ
Suwayta
2440
¦
44 BamBuAll\ \
AyunAnelali
k.
_
2430
®
24211
JabalQarari
A Ashkharah
Fig. 1. Simplified topographic map of the Batain Plain with Ihe location of measured lithologie sections discussed in Ihetext.
Roger
et al.(1991). Béchennec
et al.(1992b)
andWyns
etal.
(1992) considered
theallochthonous sedimentary units
ofthe Batain Plain
as apart
of theHawasina nappes
(sensuRobert¬
son et al.
1990).
Structural
datahowever, indicate
aWNW directed nappe emplacement with NNE-SSW trending folds
andthrusts, in contrast
to thesouth
tosouth-west thrusting direction of the Hawasina nappes (Immenhauser
et al. 1998:Schreurs
&Im¬
menhauser
1999).The WNW oriented obduction
issimilar to
theobduction direction
of theMasirah Ophiolite (Marquer et
al. 1995).Structural, biostratigraphic
andsedimentological data
suggestthat
theobduction
of theBatain allochthonous sequence onto
thenorth-eastern Oman continental margin
oc¬curred coeval with
theobduction
of theMasirah Ophiolite, at
theCretaceous/Paleogene boundary (-65 M). This
isabout
15- 20My later than
theSW-directed emplacement
of theSemail Ophiolite
and theHawasina Nappes onto
thenorthern conti¬
nental margin
ofOman (Allemann
&Peters
1992;Glennie et
al.1974).
This paper
dealswith
theTriassic succession
of theBatain Group
andsummarises
theresults
ofextensive field work
in¬cluding mapping
at the LIOO'OOO scale,logging
ofsections,
aswell
asmicrofacies analysis, biostratigraphy. sequence stratig¬
raphy
andstable isotope stratigraphy. Based
on these datawe propose
asedimentary
andstratigraphie reconstruction
ofthe proximal north-eastern Triassic Oman margin. Further,
we dis¬cuss the
contrasting evolution
of theBatain Basin which was
an
embayment
of thesouthern Tethys.
ascompared
to thatof
the
Hawasina Basin.
Geological setting
The
Batain Plain
islocated
innorth-eastern Oman, southeast
of thetown
of Sur(Fig.
1 Itextends about
130kmnortheast- southwest
and 40 kmeast-west
and isbounded
on thenorth by
theGulf
ofOman
and on the east by theArabian
sea.The Wahibah
Sandsseparate
theBatain Plain
in the westfrom
In¬terior Oman. Recent
sand andgravel deposits cover
anexten¬
sive
part
of thearea.
The
Batain Plain (Fig.
2)comprises
theBatain nappes which
arecomposed
ofPermian
toMaastrichtian marine
sedi¬ments,
aswell
asvolcanic rocks
and theEastern Ophiolite nappe. The nappes
areunconformably overlain
byAutochtho¬
nous
Late Paleocene
toMiocene continental siliciclastic and shallow marine calcareous sediments (Fig.
2).Tectonically. the Batain nappes
arecharacterised
byintense folding
andthrust¬
ing.
Outcrops
of theTriassic
seriesoccur throughout the Batain
area andtypically form brownish-grey
todark-brown weathering hills. Complete successions with minor tectonic
dis¬turbance rarely exceed several
tens ofmeters, except
forthe section found
6 kmWNW
of thelittle village
of Sal (Fig. 1)which exposes
asuccession more
than 180meters thick.
Previous work
Initial geological investigations
inOman were carried
outin
theearly
1960s by thePetroleum Development Oman (PDO)
and
Shell geologists. The classical study
of theOman Moun¬
tains
byGlennie
et al.(1974) became
the basisfor
much subse¬quent research. These authors included
theBatain sediments
in the
Late Permian
toEarly Jurassic Ibra Formation,
andthe Late Triassic
toEarly Cretaceous Haifa Formation, both part
of theHawasina allochthonous units (Fig. 3).
In the
early
1980s,Amoco Petroleum Company (Interna¬
tional) funded
amajor field-based research program
inOman.
In the
course
of thisproject (1981-1987). detailed regional
cor¬relations were established throughout
theOman Mountains
and
published
as asummary
ofalternative stratigraphie nomenclature. Bernoulli
&Weissert (1987) found that
inthe central Oman Mountains
theHaifa Formation
is LateTriassic
in age,
rather
than LateTriassic-Early Cretaceous
asproposed
by
Glennie
et al.(1974). They included
theHaifa radiolarites
in the
Al Ayn succession. Bernoulli
&Weissert (1987). Cooper
(1987. 1990). and
Bernoulli
et al.(1990) correlated
thelower
part ofthe Haifa Formation
and theHaliw Formation with the
Zulla Formation
(sensuGlennie
et al. 1974) of thecentral and
northern Oman Mountains. Furthermore. Bernoulli
etal.
Sur
Quaternary
\llu\i.il lausand terraces&
Aeolian sandveneer
Ra s .il Hadd
Sanddunes
Tertiary Maastrichtian
Batain Group
M
Sal Formation and7,
(umay/a Formation
?T
I.ih.il Jaalan
Proterozoic basement Ad DalIah
* *¦
"*
J __iRuwaydah
£« / J J * __iRu __iRu O-' C^ArRu-ays
Al
Khabb.ili
^ // l?x/ . . . . O * fer
^ ^^^
^ ^ ^ l? l x/ « l? l? l? l? ? ? x/ x x x/ x/ x/ x Musawa Mtisaua Mtisaua rr /
»Vi
fy 3
*
A
Khaddah
As
Suwayh
AseeIah
O"
Bam Bu
H'J**M
4 'JÎ Y
Al
Ashkharah Y
Fig. 2. Simplified geological map of the Batain Plain, showing the outcrop distribution of the Sal Formation and the Guwayza Formation.
(1990) equated
the AlAyn Formation
ofGlennie
et al.(1974) with
theZulla Formation
sensuCooper (1987)
anddistin¬
guished four
newlithological members within
theZulla For¬
mation (Fig. 3).
Between
1982 and 1990. theBureau
deRecherches Géologiques
etMinières (BRGM) introduced
a newlithos¬
tratigraphic nomenclature for Oman,
based ontheir
LIOO'OOOmapping program
in theCentral Oman Mountains. Béchen¬
nec
(1987) replaced
theZulla Formation
and theGuwayza Sandstone Formation
sensuCooper (1987)
in theOman Mountains (Fig.
1).with
thenewly introduced Al
Jil andMat¬
bat
formations (Fig.
3).During
asubsequent mapping pro¬
gram. Béchennec
et al.(1992a) redefined
theMatbat Forma¬
tion,
inorder
toinclude within
thelower member
asequence
ofCarnian radiolarian cherts
and shalespreviously attributed
to the
upper member
of theAl
JilFormation (Fig. 3).
Immenhauser
et al.(1998) made
anattempt
tointegrate their divergent biostratigraphic results into
thestratigraphie terminology
used on theBRGM geological
maps.They contin¬
ued,
therefore,
to use theformation
andunit
namesintroduced
by
Roger
et al.(1991). Béchennec
et al.(1992b).
andWyns et
al. 1992)for
theBatain
series, but in amodified
sense.Impor¬
tantly, they recognised significant differences between the Hawasina
series and theBatain
series anddefined
theBatain Group
for thelatter (Fig. 3).
During our subsequent studies
in theBatain
area we hadto
solve theproblem that lithologically identical rocks were
at¬tributed
byWyns
et al.(1992)
andBéchennec
et al.(1992b) partly
to theAl
JilFormation
andpartly
to theMatbat Forma¬
tion. Rather than redefining
thoseformations again
weprefer
to
establish
a newformation for certain Triassic rocks
ofthe Batain Plain, for
thefollowing reasons:
(i) the lack ofgeneral lithological
and agecorrespondence with both
theAl
Jiland
theMatbat Formation
asdefined
in theOman Mountains (Béchennec
1987:Béchennec
et al. 1992a) andwith
theZulla Formation
sensuGlennie
et al.(1974)
andBernoulli
etal.
(1990): (ii)
thecomplete missing
of agediagnostic data from
thesections known
in theOman Mountains which hampers
anydetailed correlation with our Batain
series:(iii)
the Sal sec¬tion represents
acontinuous well exposed
andwell dated
se-(ällinK-ft iL 1174
Cooper I9K7
Kt:llnlillll'|al.
1990
Béihenneeelal.
1987
BRGM 1992
1IMtW (r.**»»lmiF
1hisslud>
H d m r a t
Du
i u (i r ti i p iamrai DuruBasin BalaniGroup(flS ((
ï
n
\
\
\
E\
LU C
<
±
/
//
E
Ri\amahfm
Ì
Nayid Fm
-e Nayid Fm
Wahrahini NasKlr-m
Sid'i1in
Na>id Fm
Sid'tFm Sid'rFm
Suitlin
1 i
//
/ -a
Guuav /a LimestoneFm
Guwayza^x.
SandstoneFni^s.
illttaW.i Ini
ti.E
<
i
x:E
\
"-Sst
mb^_
GuwayzaIn (Jgw)
E
i
Ippermh (Jmb2-gw andJmbTi (iuway/a-AlAyn
Sandsionc
_f I'ppermh M
~. Lower mb
1
Lower mb (TRmbi
1nn; HalobiaKt
imt Radchert
1 ZullaFm 1
Upper mb
ë Onu2
T
u. Sandstones
&
n Shales 1
PTRaj1 Mudstonemb
E
L'mt1
Turbiditic Calcarénites&
Shales
Lowermh 1'IR.,,1, I'lR.n-1, PTRjj*
Fig. 3. Relationship between Ihe alternative stratigraphie nomenclature and the different stratigraphie subdivisions for Ihe Hamral Duru Group and the BatainGroup.
"""""
'Mh27 98/23C H561
Slh24
Slh lh
Slh 11
Mh 10
98/25C
Sth-
Sth s H606C
H6117
sih
:
I
L
notopc ...iH.Jonl A radiolaria *""
H 827R
Slh^h
H6111
Sthsli
H609C H354a
Sth4h
\ib40
Mb.U
u
radiolina -r- '
Il S7s( II614
H566
Ub82 MhSI
98/18C SthZSa
Sth -,s
H615C
II565
II 151 Mb7S 98/17C Mb73
n/47 II 7s;
Mbh9
H613
Mb66 H612C
Mb6S H353
Mb64
H828R
H611
Limestone Sandvlimestone Packstone.Grainstone Silicified limestone
Radiolarianlimestone Wavy / platy bedded limestone Oolitic limestone Microbreccia
Conglomerate, matrix supported Conglomerate, clast supported
Fining upwardconglomerate and breccia beds Sandstone
Calcareous or marly shales Siliceous shalesand claystones Radiolarian-bearinü chert
Ribbon-bedded chert
1 i t
1 1
S
-ry^r
...l...ry r ry r ^
1 aa t.11 -
Sas
i -
s 1 s
AAA
1 s 1
Fig.4. Lower part of the lithostratigraphic section of the Sal Formation at the locality 1 (762478/2449654) 7 kmWN of the village ofSal.
quence encompassing nearly
theentire Triassic. This
newfor¬
mation
(SalFormation)
isdefined
at thelocality
7 kmWNW
of the
village
Sal(762478/2449654), (Fig.
1,locality
1).1.
Lithostratigraphy ofthe
SalFormation
The Sal
Formation
issubdivided from
base totop into three mappable members ranging
in agefrom Scvthian
toRhaetian (Fig.3).
Mudstone Member: This
50mthick member consists of grey-brown
flaggylimestones, calcilutites
andpartly silicified
pale green to
yellowish calcareous
shales andclaystones.
Itwas considered
as theuppermost part
of theAl
JilFormation by Roger
et al.(1991). Béchennec
et al.(1992b).
andWyns
etal.
(1992).
Chert Member: This
is 15mthick
andcomprises purplish-
red and
greenish radiolarian cherts with shaly partings, pale green
toyellowish claystones
andinterbeds
ofstrongly silici¬
fied radiolarian-bearing limestones.
Calcarenite Member: This member consists
ofbrownish, partly silicified calcarénites with thin-shelled pelagic bivalves
(filaments), alternating with radiolarian-bearing cherts and mudstones.
andsiliceous
orlimy
shales.Isolated calcirudite
in¬terbeds
are alsopresent.
Theestimated thickness
of thismem¬
ber
varies from
115 up to 150m.
The
newly defined Chert
- andCalcarenite members are equivalent
tounits mapped
as thelower member
of theMatbat Formation (Trmbl)
on the sheet 1:1(K)'(X)()Ja'alan (Roger et
al. 1991) and the sheets
1:250'000
ofAl Ashkharah (Béchen¬
nec et al. 1992b) and Sur
(Wyns
et al. 1992). Based onlithology
and age. we assign
their upper Matbat member (Jmb2)
and un¬differentiated Matbat
andGuway/a Formation (Jmb2-gw) to
theGuwayza Formation (Fig. 3).
The
lower formation boundary
of the SalFormation
(Fig.4)
is
defined
at the typelocality
at the base of theMudstone Member, previously considered
as theuppermost part
ofthe Al
JilFormation
byRoger
et al.(1991), Béchennec
etal.
(1992b)
andWyns
et al.(1992).
Aprimary stratigraphie con¬
tact
between
theMudstone Member
and theAl
JilFormation
as
shown
byBéchennec
et al.(1992b)
is notexposed
inthe Batain Plain.
ÜL^al "'
1" -
H843 H843C
llll
112? 0/45
0/46
Slh 122 98/2IC
H842C
98/20C
H834C
Mh
III)
SlhHIS H836C
\lh HIS
1104
Mb103 Mb100
1 99.5
1//)9 s
1=^.
<><c
A
t> -tt
nhis:
SlhISII
sii-1\-
HH2H
\lhlh9
Il Siti Mbi 7v
MblS7
HH3I
Il832C
H833C
10m
5ni
unbedded shales
1 ' beds <Scm
...¦.=.'; beds >5 cm< 10cm
Om
'X, Pelagic bivalves
Shell hon/oniol pelagicbi\ahes
(> Filaments
M Radiolarian^
w
Conodonts¦Ù! Crinoids
&
ForaminiferaQ> Ammonoids
Qz Oliali/
l
finingupParallellaminatimi
.n
Rippleteckmi/ed
Fig.5. Upper part of the lithostratigraphic section of the Sal Formation at the locality 1 (762478/2449654) 7kmWN of the village ofSal.
B
Locality
4(777672/2455271)
Locality
2(763489/2426800)
40ni
L
<u
O
"
I I
H 513
K H 512
\ Mi-
nini
ft H 5I1
i ft H 5I0 I
I a H
5/10
A H 5/7
ft H
5/6
ft H
5/5
ft H 5/1
H 504
H 508
Fig. 6 A. Lithostratigraphy of a part of the cal¬
carenite Memberof the Sal Formationdominated
by the characteristic filamentous limestones and Earlv Carnian radiolariancherts.
B) Detailed section of a part of the Calcarenite Member wilh Early Ladinian to Early Carnianra¬
diolarian cherts and microbrecciainterbeds.
The
upper formation boundary
isexposed
at thelocality
3
km
SW ofAseelah (769662/2428915) (Fig.
1.locality 2).
There,
theCalcarenite Member
of the SalFormation
isover¬
lain by the
Guwayza Formation.
TheGuwayza Formation
isdistinguished from
the SalFormation
by thepresence
of cal¬careous sandstones
andoolitic calcarénites devoid
ofpelagic bivalves.
The
composite lithologie section
of the SalFormation ranges from
theSpathian
to theRhaetian
basedmainly on conodonts.
The
Mudstone
and theChert Members
arewell exposed at
the typelocality (Fig.
4 and Fig. 5).This section shows
the con¬tacts
between
theMudstone
andChert Members
aswell
asthe contact between
theChert
and theCalcarenite Members. The Calcarenite Member
at thetype locality consists mainly
of alimestone-dominated facies. whereas
in thesections
atlocali¬
ties
north
of AlAshkahrah (763489/2426800) (Fig. 6A) and northeast
ofRuwaydah (777672/2455271) (Fig. 6B) filamen¬
tous
limestones, radiolarian-bearing cherts
and shales arealso present.
The
Chert
andCalcarenite members contain several meter-
thick lamprophyre
sills,basaltic flows
andgabbro intrusions.
At
alocality
8 kmWSW
of Sal(760260/2444889),
agabbro
in¬trusion produced
acontact aureole
in theneighbouring lime¬
stones that contains tremolite pseudomorphs.
The
Mudstone Member
This lowest member
of the SalFormation
iswidespread
inthe middle
andsouthern part
of theBatain
area. Ittends
tooccur
at the
foot
of thehills built
up by the SalFormation.
At
thetype locality (Fig.
4). theMudstone member mea¬
sures 50 m.
The member starts with
30 m ofbeige-grey platy.
wavy-bedded mudstones
andvery fine-grained calciturbidite.
interbedded with yellow-brown calcilutites. marls
andcalcare¬
ous shales.
The centimetre-thick turbidites consist
ofincom¬
plete, base-cut-out Bouma
Tc-Tesequences with erosive basal contacts.
Thepredominant sedimentary structures
areripple cross-lamination, hummocky cross-bedding
and in some beds amillimetre
tocentimetre-scale planar lamination.
Solemarks
are
rare,
butisolated flute
casts wererecognised.
The flaggy limestones
areconformably overlain
byless
than
20 m ofthinbedded pale-green claystones
andsilty shales with intercalations
ofcentimetre-thick
beds ofgrey-brown mudstones
and raresandy limestones (Fig.
4).The Mudstone member
endswith
a onemetre thick horizon
ofnodular, thin¬
bedded
andweakly laminated limestones, containing rare
lay¬ers of
thin-shelled bivalve filaments.
In some of these beds aweak bioturbation
isobserved. At
thesurfaces
of some ofthe nodular limestone
bedsferrugineous crusts
andmillimetre-
sized
nodules occur.
Microfacies
andage
The
dominant microfacies
of thelimestones
isahomogeneous, sometimes thinly laminated, mudstone (microsparite) contain¬
ing
millimetre thick coquinas
ofostracods
andconodonts. The thinner bedded
andrippled calciturbidites
aremade
up ofbio¬
clastic packstones
andgrainstones with worn bioclastic grains, calcite-replaced radiolarians. small ostracods, echinoderms.
rare
benthic foraminifers (Nodosariidae)
andpeloids.
The lower part
of theMudstone member
has beendated
asLower Triassic (Spathian)
on the basis oftwo ammonoid hori¬
zons
with Dieneroceras
cf.mediterraneum
and theconodont assemblage (H606,
98/25, 98/23)(Tab.
1).whereas
thetop of
the
Mudstone member
is ofMiddle Anisian (Bithynian) age, dated
byconodonts (H609C). (Tab. 1).
The
Chert Member
The 15 m
thick Chert member
ismade
up of 1 to 10 cmthick, regularly bedded
palegreen
toyellowish claystones, purple
and
copper-green radiolarian cherts with
shalypartings
and in¬terbeds
ofstrongly silicified radiolarian-bearing limestones.
At locality
6 kmWNW
of Sal(Fig.
1), onesingle
2-3cm thick tuff layer
wasfound within
theChert member, whereas about
5km
SE ofAyun (761047/2435522). lm thick lapilli-
bearing tuff
ispresent within approximately
15 m ofradiolari¬
an
cherts.
Microfacies
and ageThe
microfacies
of theChert Member
iscomposed
ofradiolar¬
ian
cherts
andradiolarian packstones, silicified grainstones with echinoderm fragments, filaments
ofpelagic bivalves and
rareNodosariidae. The clay-rich siliceous matrix
of themud
andpackstones contains abundant radiolarian moulds.
The
radiolarian fauna
of theChert member
is ofLate Anisian
age(H827, H828) (Table 2).
The
Calcarenite Member
The radiolarian cherts
of theChert Member gradually
passup¬ward into
acarbonate-bearing succession
of theCalcarenite Member, whose estimated thickness
is at least 100 m(Fig. 4
and Fig. 5).The lower
15 mofthe Calcarenite Member consist
ofmainly
10 to 40 cmthick
beds ofbrownish calcarenite, greenish shaly marls
andradiolarian-bearing mudstones and cherts. They
areoverlain
bymore than
20m ofsiliceous shales
and
cherts without well developed limestone
beds. Theshales gradually
passupwards into
asequence
ofalternating siliceous
shales,radiolarian micrite. calcarenite
andfilamentous lime¬
stones.
The
limestone
bedsshow
abrown
toblack patina.
Inplaces
they aresilicified
andconsist
ofplanar laminated calcarenite
and ofincomplete Bouma
Tb-Tcturbidites.
Thelaminated
cal¬carenite
and thefilamentous limestones
arecharacterised by
the
presence
ofcentimetre-thick layers
ofthin-shelled pelagic bivalves
of theHalobia-Daonella type. At
thetype locality (Fig.
4 and Fig. 5) andNE
ofRuwaydah (777672/2455271) (Fig. 6B).
theCalcarenite Member contains interbeds of polymict calcirudite that
are a few to 20 cmthick.
At locality
6, 3km
SW ofAseelah (Fig.
1) theuppermost
60 m of the
Calcarenite Member contain
acentimetre to decimetre thick, poorly bedded calcarenite-calcsiltite-shale succession. The
bedsshow
athinning-up trend, plane lamina¬
tion, ripples
andisolated slump structures.
Thequartz content
in the
limestones
and theproportion
of shalesincreases
up¬section.
TheCalcarenite Member grades conformably upward into
theoverlaying Guwayza Formation.
The predominant sedimentary structures within
theCal¬
carenite Member
aremillimetre thick parallel laminations and swaley cross-stratification similar
tohummocky cross-stratifi¬
cation. Weakly fining-
andthinning-upward sequences were
alsofound within
thecalcarénites. The cross-stratification
ischaracterised
bylow amplitude ripples
(1 to 3cm) undulating
as a series of
broad anticlines
andsynclines. The ripples are
made up ofwispy indistinct laminae which frequently thicken
in the
anticlines
andpinch-out
in thesynclines
or passlaterally into plane laminations.
Microfacies
andage
The
microfacies
of theCalcarenite Member consists
ofplanar laminated limestones,
andthin bioclastic grainstones
andpack¬
stones
(biopelmicrosparite
tosparite), which yield
massesof oriented thin-shelled valves
ofHalobia-Daonella type, togeth¬
er
with recrystallised radiolarians, abundant foraminifera (No¬
dosariidae)
andmicritic peloids
(seeGlennie
et al.1974:
Shackleton
et al. 1990;Béchennec
et al.1992b). The radiolari¬
ans are
often strongly recrystallised
and notidentifiable.
The
cross-stratified
Tcturbidite
beds,made
up ofweakly graded grainstones
andpackstones with wackestone
tops(cal¬
carénites), consist
ofreworked fine-grained litho-
andbio¬
clasts,
deposited within distinct lenticular layers. These layers
areoften separated
bymillimetre-thick laminated lime mud.
The
carbonate detritus consists
ofsmall, worn bioclastic grains, peloids,
andrare ooids. The bioclasts include benthic foraminifera (Tab.
3).ostracods, gastropods,
andremnants of echinoderms
and algae.These shallow-water elements
inthe detritus were derived from
ashallow carbonate ramp environ¬
ment.
Awell preserved autochthonous population
ofcon¬
odonts
(Pl. 1) andfilaments were
alsoobserved
inthin section.
They
areassociated with allochthonous conodonts. reworked
from
theproximal
basinfloor during their transport into the distal part
of thebasin.
Unsorted polymict calcirudite interbeds
arecomposed of angular
torounded, millimetre-
toseveral centimetre-sized
clasts and
boulders, supported
by asparite cement.
Theclasts
aremade
up ofreworked carbonate litho-
andbioclasts, vol¬
canic clasts
andchert fragments. Identifiable fossils include foraminifera. small gastropods, ostracods. remnants
ofalgae
andechinoderms: coral fragments
andembryos
ofammonites.
The calcirudite
alsocontains Permian bioclasts. with fragments
ofFusulinids
andBryozoans.
The conodont, radiolarian,
andforaminiferal assemblages (Tab. 1-3) indicate
aLadinian
toRhaetian
agefor
theCal¬
carenite Member.
2.
Biostratigraphy Conodonts
The
SalFormation contains abundant conodonts with
alow CAI index
of 1 in theMudstone
andCalcarenite members.
The Chert Member
maycontain conodonts but
was not sam¬pled
due to theabsence
oflimestone intercalations.
Conodonts from
theMudstone Member
arewell pre¬
served, relatively small
anddominated
byspecimens
ofthe
genusNeospathodus. They
arccompletely preserved, including
the
delicate
ends of theteeth,
and aretherefore interpreted
asautochthonous, although transport
by mudturbidites
ordistal tempestites within
asoft matrix
can not beexcluded. Within
the
Calcarenite Member, only
thefilament-and radiolarian- bearing wackestones
(e.g.H834, H842, H832) contain
au¬tochthonous conodonts. All sampled calcarénites (pack- and grainstones) contain conodonts
ofhighly varying
agesinclud¬
ing even
Permian
species(Tab.
1).These samples
arerich in large platform conodonts which
areoften fragmented
andonly rarely well preserved. The
agedetermination
of thecalcarenite samples
was based on theyoungest occurring conodonts which
are
usually much more common
thanreworked
ones.The age range
ofreworked conodonts increases up-section, document¬
ing
increasing erosion
andredeposition
ofintrabasinal sedi¬
ment. The reworked conodont fauna
iscomposed
ofPermian (Roadian-Wordian) gondolellids, Early Triassic neospathodids
andMiddle
toLate Triassic Neogondolella. Gladigondolella.
Metapolygnathus
andEpigondolella
species.Records
ofLate Permian
andlowermost Triassic conodonts
arecompletely missing
and it may bethat sediments
of this agewere either not deposited
or wereremoved prior
to thedeposition
ofthe
Sal
Formation. Redeposition
ofPermian sediments near the Permian/Triassic boundary
may be adistinct feature
ofproxi¬
mal
basin parts
of theOman allochthon
(e.g.Wadi Wasit area -Blendinger 1988).
Biochronological dating
of thesamples
is based oncon- odont-ammonoid calibration schemes
byOrchard (1995) for
the
Early Triassic, Nicora (1977)
andKrystyn
inGallet
etal.
(1998) for
theMiddle Triassic
andKrystyn (1980)
aswell
asKrystyn
inGallet
et al.(1994) for
theLate Triassic.
The baseof
the
section (H606)
and theoverlaying calcareous part
ofthe Mudstone Member (98/23. 98/25)
aredated
by N. cf.homed
(Pl. 1. Fig. 5), N.
sytnmetricus
and N. cf.abruptus
(Pl. 1. Fig.8)
as
Spathian.
98/25 alsoyields
N. cf.jubata.
Thenext fossilifer¬
ous
sample H609 from
20m abovecontains
/V. cf.regularis.
adistinct Anisian (Bithynian) form.
Noconodonts
areknown from
the shalyinterval
inbetween which, according
to its posi¬tion,
istentatively attributed
to theEarly Anisian (Aegean).
Conodonts
are alsomissing from
the 15msuccession
ofradio¬
larian cherts dated indirectly
by thefaunas below
H609and above H612 (Fig.
4B. C).The succeeding limestone-shale
se¬quence
of theCalcarenite Member contains
N. cf.praeszaboi
at its base(H612) which
isthought
torepresent
the basalIllyrian.
Just 3m
above, sample
(0/47)contains
P. excelsa, N.transitu and
B. cf.hungaricus recording
aLate Fassanian
age.Four metres above (98/17),
P.inclinata.
P.trammeri
(Pl. 1, Figs.9,15)
andB.
hungaricus occur, recording
anearly Late Ladinian (Longobar¬
dian)
age. Thetopmost Anisian
andEarly Ladinian
are,there fore, very condensed. An early Late Ladinian
age isfurther
in¬dicated
inH615
by thepresence
of B.japonicus. Samples 98/18
and H835contain
P.inclinata
and B.mungoensis
(Pl. 1. Figs. 2.14) and are thus of
Middle
toLate Longobardian
age.Between
H835 and thefirst Carnian sample
H836,more
than 20 m of un¬dated siliceous
shaleswithout
welldeveloped limestone beds
arepresent. Consequently,
we haveinterpolated
theLadin- ian/Carnian boundary halfway
inbetween. This procedure
isstrengthened
by the age ofsample H836 which
isplaced strati¬
graphically well above
theboundary
as itcontains
M.cartiicus
(Pl. 1, Fig. 11). a speciesdiagnostic for
themiddle part
ofthe Early Carnian (Gallet
et al. 1994). Theother Early Carnian samples H836, H834,
98/20.H842
and 98/21 aremarked by Gladigondolella,
M.polygnathiformis
(Pl. 1, Fig. 13) and M.fo-
Hants,
sample
H842 alsocontains
M.auriformis
(Pl. 1. Fig.12).
The Lower/Upper Carnian boundary
isdrawn directly above
98/21 sincesample
0/46located
3 mhigher
upyielded
arich
andexclusive Metapolygnatus fauna composed
ofM.
polygnathiformis
andsubordinate
M.carpathicus
(Pl. 1. Fig.6).
The latter
is adistinct guide for
theMiddle Tuvalian, hence
ahiatus
may exist in the basalTuvalian.
AMiddle Tuvalian age
is
further indicated
bysamples
0/45 andH843. The succeeding
20 m
thick uppermost Carnian (Tuvalian
3) and 25 mthick lowermost Norian (Lacian
1)intervals
are bestdocumented by conodont faunas. Sample H833 still contains
M.polygnathi¬
formis
(Pl. 1. Fig. 13) and M.nodosus
(Pl. 1, Fig. 10).whereas H832
and H831 arelatest Tuvalian
asdemonstrated
bythe presence
of M.oertlii
and M.communisti A-type sensu Krystyn (1980)
(PI. 1, Fig. 7). The baseofthe Norian
ismarked
in
sample
H 830 by theappearance
of N.navicula
(PI. 1.Fig.
1
which
is alsopresent section upward
insamples H829 and H828. Still earliest Norian
isrecorded
insample H616
by E.quadrata,
a date inaccordance with
theco-occurring Halobia
cf.
styriaca.
apelagic bivalve guide
for theLacian
1.Although younger Norian rocks
aremissing
in the Sal sec¬tion,
the samelithology
seems to havecontinued towards the
WNW
I SIs769672/2421(69;
Guwayza Formation
Sal
Formation
'
t, tectonized
H 876
762478/244>)6S4
4
2
Calcarenite Member
767487J/2426XOO
777672/24SS271 ¦
\ \
5
* \ K17\
_\ H 508/ /
N
/
Mudstone
Member proximal
Chert
Member
distal
Fig. 7. Triassic stratigraphv and facies variations ofthe
Sal Formation in the Batain Plain showing an increase of radiolarian cherts from proximal to distal parts ofthe basin.
top of the
Triassic
asdocumented
inanother outcrop (section
6 in
figure
7).Here,
anearly Rhaetian fauna consisting
ofM.
hernsteini
and M.posthernsteini
ispresent accompanied
by re¬worked Permian
andNorian conodonts. Reworked conodonts
arerepresented
in the Salsection from
theLadinian onwards.
The
samples H830
and H831contain Permian
(Pl. 1. Fig. 3) aswell
asEarly Triassic
(PI. 1. Fig. 4).Middle
andlower Late Tri¬
assic
forms. Sample H835 yields Permian
toMiddle Triassic reworked forms, samples
98/17.H836.
andH828 Permian and Early Triassic reworked conodonts. Sample
98/21contains only Lower Triassic reworked conodonts whereas H615 Mid¬
dle
Triassic displays reworked forms. Samples
98/18 andH842 contain only Permian forms.
Radiolarians
Radiolarians
of the SalFormation cover
astratigraphie inter¬
val
from Late Anisian
toMiddle Norian (Tab.
2).Their occur¬
rence corresponds
to thelevels
ofradiolarian cherts
ofthe Chert
and theCalcarenite Members.
Thepreservation varies from
verypoor
tomoderate
and thenumber
ofspecies deter¬
mined
isusually small. Fortunately, many diagnostic species with Lagile
tests haverobust
spinesresistant
todissolution which allows species determination.
Inorder
toestablish the
age of
radiolarian assemblages
we usedespecially
thezonation
schemes established
byKozur
&Mostler (1994)
for theLate Anisian
-Early Norian interval,
and byBlome (1984) for the Early
-Middle Norian.
The Late Anisian-Early Longobardian interval
canbe recognised
andsubdivided
by therepresentatives ofthe family Oertlispongidae. whose evolution
andradiation took place particularly within
thisinterval (Dumitrica
1982:Kozur &
Mostler
1994. 1996:Lahm
1984,etc.). This family, charac¬
terised
by thepresence
ofahighly differentiated polar spine,
is one of the mostimportant radiolarian families for
thestratig¬
raphy
of theTethyan Ladinian
andfor determination
ofthe Anisian/Ladinian boundary (Kozur
1996).The advantage of
using
thisgroup
ofradiolarians
isthat
thediagnostic polar
spines are
very resistant
todissolution
and arepreserved even
in the
poorest preserved faunas.
The
oldest radiolarian assemblage
of the SalFormation
was
found
in thesection
at thetype locality (Fig.
4)(H827)
(Pl. 2. Figs.
1-2)
and isconsidered Late Anisian
in age. It isvery poorly preserved, represented
by somespecimens of Eptingium manfredi, Pararchaeospongoprunum
cf.henni, and especially
by spines ofoertlispongids with widened distal part.
These
spines wereassigned
toParoertlispongus multispinosus whose first appearance
isrecorded
in theLate Anisian Parac¬
eratites trinodosus Zone (Kozur
1996).Although this type of
spine