Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
149
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
Lucia Angiolini, Sylvie Crasquin-Soleau, Jean-Pierre Platel, Jack Roger,Daniel Vachard, Denis Vaslet and Moujahed Al-Husseini
ABSTRACT
Along the western flank of the Haushi-Huqf Upift in Oman, the upper Palaeozoicsuccession consists of (from oldest to youngest): (1) glaciogenic Upper Carboniferous-Lower Permian Al Khlata Formation; (2) marine Lower Permian Saiwan Formation (=Lower Gharif Member of subsurface Oman); (3) continental Lower and Middle Permianredefined Gharif Formation (= Middle and Upper Gharif members of subsurface Oman);and (4) lower part of the Middle Permian marine Khuff Formation. The successionoverlies lower Palaeozoic-Proterozoic rocks, and the Khuff Formation is truncated byTriassic and younger unconformities. The Al Khlata Formation is about 100 m (328 ft)thick, and consists of a succession of diamictite, sandstone enclosing pebbles to bouldersof sandstone, dolomite, black chert and pink granite clasts (ranging in diametre from afew centimetres to a metre). The overlying Saiwan Formation comprises two bioclasticunits: lower ‘Bellerophon Limestone’ (10-18 m, 33-59 ft thick) and the upper‘Metalegoceras Limestone’ (35-40 m, 115-131 ft thick). A basal Pachycyrtella Bed of theSaiwan Formation yielded Pachycyrtella omanensis associated with subordinatespecimens of the genus Strophalosia indicating a mid-Sakmarian age. Brachiopod,ammonoid and bivalve assemblages in the main part of the Saiwan indicate a lateSakmarian age. The Saiwan Formation contains (5 metres above its base in the typesection) Arabian Plate Maximum Flooding Surface MFS P10 of late Sakmarian age,and based on the latest Permian time scale is recalibrated at about 284 Ma (previously272 Ma).The redefined Gharif Formation (70-100 m; 230-328 ft) lies unconformably abovethe Saiwan Formation, and consists of shale and sandstone deposited in floodplainand ephemeral shallow-lake environments. Uppermost Gharif ‘estuarine’ subunit Blies conformably below the first marine Khuff deposits, and contains a rich macroflorathat is not diagnostic of a precise age, but is considered ?Roadian-?early Wordian. Theincomplete Khuff Formation (30 m, 98 ft) consists of three informal members (1-3 frombase up). The transition from Gharif subunit B to lowermost Khuff member 1 representsan environmental change from a distal fluviatile/estuarine system bordering a coastalplain, to a clastic transgressive shoal/barrier environment. Khuff members 2 and 3reflect a carbonate shelf environment. The lower sequence boundary of the Khufftransgression is interpreted to be at the base of Gharif subunit B. Marine fauna in theKhuff Formation includes cephalopods, brachiopods, conodonts, ostracods andbivalves, which indicate a Middle Permian Wordian age. Conodont fauna from theuppermost levels of Khuff member 3 suggests a late Wordian age. The foraminiferaindicate a Middle Permian age (Wordian and Capitanian).
INTRODUCTION
Along the western flank of the Haushi-Huqf Uplift (also Arch or High) in Oman, Upper Carboniferous-Middle Permian rocks outcrop in a SW-trending belt, and are mapped as the Al Khlata, Saiwan, Gharifand Khuff formations (Figure 1; Dubreuilh et al., 1992; Platel et al., 1992, Roger et al., 1992; hereaftercombined where appropriate as BRGM, 1992). The Permian Khuff Formation, in this region, is truncatedby several unconformities starting with the overlying Triassic Minjur Formation (Figure 2). Theseoutcropping units pass, in part, to the subsurface Al Khlata, Gharif and Khuff formations of InteriorOman (Hughes Clarke, 1988; Osterloff et al., 2004a, b). The outcropping Saiwan Formation becomesthe subsurface Lower Gharif Member; it was renamed by BRGM (1992) to highlight a regional angularunconformity at its top (supra-Saiwan unconformity, Figure 2), which is manifested in south and eastOman (Blendinger et al., 1990; BRGM, 1992; Osterloff et al., 2004b).
The stratigraphic record in this region represents the following four depositional phases: (1) Al KhlataFormation reflecting the Late Carboniferous-Early Permian glaciation of southern Arabia (Arabian Plate
Angiolini et al., 2004
150
Figure 1: The Al Khlata and Saiwan formations (Haushi Group sensu BRGM), and Khuff and redefinedGharif Formation (Akhdar Group sensu BRGM) outcrop along the western flank of the Haushi-HuqfUplift (also Arch or High). The Proterozoic to Cambrian Huqf Supergroup outcrops over the NE-trendingHaushi-Huqf Uplift along the Arabian Sea. The Haushi-Huqf region was mapped in three areas byBRGM in 1992: Duqm and Madraca (18.8°-20°N; Platel et al., 1992); Khaluf (20°-21°N; Dubreuilh et al.,1992); and Mafraq (21°-22°N; Roger et al., 1992).
Khaluf
Sirab
58 30'
57
Mafraqmap area
Khalufmap area
Duqm and Madracamap area
Huqf
JiddatAl Harrasis
Haushi
Arabian Sea
N30
km
0
Duqm
57
Hayy
Fiem
57 30' 58
58 30'
21
20 20
21
Saiwantype section
57 30' 58
19 30'
20 30'
20 45'
20 15'
19 45'
19 30'
20 30'
20 45'
20 15'
19 45'
Norther
n Cliff
Saiwan-1
Haush
i-Nafu
nF
au
lt
Wadi Al Khlata
Fars Group (Miocene-Pliocene)and Quaternary
Dhofar Group (Oligocene-Miocene)
Hadhramaut Group(Palaeocene-Eocene)
Aruma Group
Triassic-Late Cretaceous
Akhdar Group (Permian)(Khuff and redefined Gharif fms)
TERTIARY
END-CRETACEOUS
ARABIAN PLATFORM
Haushi Group (late Palaeozoic)(Al Khlata and Saiwan fms)Haima Supergroup andThumaylah fm (early Palaeozoic)Huqf Supergroup and (latestProterozoic to Cambrian)
Al Jobah granodiorite
Major anticline
Major fault
Limit of sand dunes
PRE-MIDDLE PERMIAN BASEMENT
CRYSTALLINE BASEMENT
Haushi-Huqf Uplift, Oman
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
151
Glaciation 3, AP G3 of Sharland et al., 2001); (2) Saiwan Formation (subsurface Lower Gharif Member)representing the first Early Permian post-glacial marine flooding (Maximum Flooding Surface MFSP10, Sharland et al., 2001); (3) a late Early and early Middle Permian period of continental depositionseen in the redefined Gharif (subsurface Middle and Upper Gharif members); and finally (4) the startof the Middle Permian transgression (Khuff and coeval rock units). These four phases prevailed overmost of southern Arabia and are recognized in the Wajid, Unayzah and Khuff formations of SaudiArabia (e.g. Evans et al., 1991).
Figure 2: The outcrop stratigraphic scheme of BRGM (Debreuilh et al., 1992; Platel et al., 1992; Roger etal., 1992) that is adopted in this study, is compared to the subsurface stratigraphic scheme (HughesClark, 1988; Osterloff et al. 2004a, b). Note the definitions of the Haushi and Akhdar groups areinconsistent between subsurface and outcrop. The Permian Khuff Formation in this region is truncatedby several unconformities. The geological time scale is adopted from Jin et al. (1997).
CHRONOSTRATIGRAPHY Ma
TRIASSIC ICS (2002) RUSSIA TETHYS
Changh-singian
Sudair Fm
Wuchia-pingian
Capitanian
Wordian
Roadian
Kungurian
Artinskian
Tatarian
Kazanian
Ufimian
Dora-shamian
Dzhulfian
Midian
Murgabian
Kuber-gandian
Bolorian
Mid
dle
(Gua
dalu
pian
)E
arly
(C
isur
alia
n)
PE
RM
IAN
Late
(Lo
ping
ian)
Sakmarian
Asselian
CARBONIFEROUS
251.1± 3.6
253.0± 0.3
264.1± 2.2
272.2± 3.2
280.3± 2.6
290.6± 3.0
INTERIOROMAN HAUSHI-HUQF UPLIFT
KhuffFormation
UpperGharif
Member
member 3member 2
member 1 unit Dunit C
subunit B
subunit A
Triassic andyounger
unconformities
MiddleGharif
Member
?
LowerGharif
Member?
'HaushiLimestone'
supra-Saiwan unconformity
SaiwanFormation
'Metalegoceras Lst''Bellerophon Lst'
Pachycyrtella bed
Rahab shale
Al Khlata Formation
Hau
shi G
roup
Hau
shi G
roup
Akh
dar
Gro
up
Akh
dar
Gro
up s
ensu
BR
GM
(19
92)
rede
fined
Gha
rif F
orm
atio
n
lower unit
uppe
r un
it
DS P17
DS P15
DS P10
DE
PO
SIT
ION
AL
SE
QU
EN
CE
P13
AR
AB
IAN
PL
AT
EG
LA
CIA
TIO
N 3
(AP
G3)
mfs
MFS P10284 Ma
ARABIANPLATE
Carboniferous-Permian Stratigraphy
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152
This paper starts with a brief review of the Al Khlata Formation (for a more detailed review see Osterloff etal., 2004a). This is followed by a detailed and updated overview of the lithostratigraphy, depositionalenvironment, sequence stratigraphy, fossils and age of the Saiwan, redefined Gharif and lower part of theKhuff formations. This overview provides important stratigraphic constraints on the depositional historyof the hydrocarbon-bearing Unayzah, Gharif and Khuff formations on the Arabian Plate.
HAUSHI AND AKHDAR GROUPS
The Haushi Group was first defined in the north of the Haushi-Huqf Uplift by Hudson and Sudbury(1959). Hughes Clarke (1988) and Petroleum Development Oman (PDO) (Osterloff et al., 2004b) adoptedthis group’s definition that combines the Al Khlata and Gharif formations (Figure 2). In contrast, BRGM(1992) define the Haushi Group to comprise the Al Khlata and Saiwan formations, the latter beingequivalent to the Lower Gharif Member (Figure 2). The difference in where to place the upper boundaryof the Haushi Group is caused by the identification of a significant unconformity at the top the SaiwanFormation (supra-Saiwan unconformity, Figure 2) (Blendinger et al., 1990; BRGM, 1992). The supra-Saiwan unconformity constitutes an important surface in understanding the stratigraphic frameworkof the Arabian Plate. According to Le Métour et al. (1995), the unconformity has a regional dip of 10o-15o and possibly marks a hiatus in the Early-Middle Permian, Artinskian-early Roadian (Angiolini etal., 1997, 2001).
The redefinition of the Lower Gharif Member as the Saiwan Formation (BRGM, 1992) cascaded severalother redefinitions that encompass much of the Carboniferous-Permian lithostratigraphic scheme inthe Haushi-Huqf Uplift; namely (Figure 2):
(1) Redefinition of the Lower Gharif Member as the Saiwan Formation;(2) Limitation of the redefined Gharif Formation to the Middle and Upper Gharif members;(3) Inclusion of only the Saiwan Formation together with the Al Khlata Formation in the Haushi
Group sensu BRGM (otherwise the group comprised the Al Khlata and Gharif formations,Hughes Clarke, 1988); and
(4) Inclusion of the redefined Gharif Formation (Middle and Upper Gharif members) in the AkhdarGroup sensu BRGM.
The above redefinitions are carried in parallel with the subsurface definitions; i.e Saiwan = LowerGharif Member, and redefined Gharif Formation = Middle and Upper Gharif members.
AL KHLATA FORMATION
Hughes Clarke (1988) credited B.K. Levell, J.H. Braakman and K.W. Rutten (1982 PDO Report) andLevell et al. (1988) with the definition of the type section of the Al Khlata Formation. Hughes Clarkereported that this type section is located at Wadi Al Khlata near the Huqf Arch (57o25’46”E, 19o46’43”N;Figure 1) where it is about 100 m (328 ft) thick. This type section, however, was not described in Levellet al. (1988), but is referenced to some degree by Besems and Schuurman (1987).
The Al Khlata Formation was mapped in three areas at a 1:250,000 scale by BRGM (1992). In outcropson the western flank of the Haushi-Huqf Uplift, the deposits are considerably thinner than in thesubsurface and possibly no more than 100 m (328 ft), compared to 100-800 m (328-2,624 ft; Osterloff etal., 2004a). Measured Al Khlata Formation sections (Figure 3; BRGM, 1992) indicate a succession ofdiamictites of grey to beige sandstone enclosing pebbles to boulders of white to green sandstone,dolomite, black chert and pink granite, ranging from a few centimetres to a metre in diametre. Thecoarsest deposits are associated with sandy conglomerates and cross-bedded, coarse-grained sandstonethat contains gravel and layers of silty-claystone and locally contorted shale. They are characterised bya topography of gently rounded buttes from which boulders are eroded that can be several metresacross. Ferruginous crusts in the form of festoons highlight the grain-size differences between the verycoarse facies and the commonly grey-beige to blue-grey, claystone-siltstone, fluvio-lacustrine facies(BRGM, 1992). At Saiwan, the uppermost part of the formation consists of red fine-grained sandstonesand green siltstones ascribed to the Rahab shale by Roger et al. (1992, p. 13) and described as an equivalentunit by Angiolini et al. (2003a).
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
153
The Al Khlata Formation unconformably overlies much older Palaeozoic rocks. East of Jebel Murqayshthe Al Khlata Formation rests on a striated pavement scoured across the top of the upper ProterozoicKhufai Formation (Debreuilh et al., 1992; Platel et al., 1992). In the Mafraq map area, the Al Khlatadeposits rest unconformably on the lower Palaeozoic Haima Supergroup, and the Cambrian-ProterozoicHuqf Supergroup. The top of the Al Khlata Formation passes unconformably into fossiliferous sandstoneof the overlying Saiwan Formation.
The Al Khlata Formation consists of a glacial-fluvioglacial complex attributed to the Gondwananglaciation (Braakman et al., 1982). On the basis of palynology, these deposits are attributed to the LateCarboniferous (late Westphalian (Moscovian)) to Early Permian (Sakmarian) (Braakman et al., 1982;Besems and Schuurman, 1987; Hughes Clarke, 1988; BRGM, 1992; Stephenson, 1988; Stephenson andFilatoff, 2000; Stephenson, 2004).
SAIWAN FORMATION
Lithostratigraphy
The Saiwan Formation (Figure 4; Debreuilh et al., 1992) unconformably overlies the diamictite andsilty shale (presumed Rahab shale of the Al Khlata Formation) and combines all the fossiliferous marinebeds informally named the ‘Haushi Limestone’ (Hudson and Sudbury, 1959; Blendinger et al., 1990).
Yellow, fine-grained, laminated sandstone
Diamictite containing large blocks of dolomite, granite, sandstone, stromatolites
White to red, fine-grained sandstone; thin beds of coarse-grained sandstone
Small-block diamictite
Beige siltstone and claystone
Dolomite substratum with striated pavement
Sandstone, red granite and black chert bearing diamictite
Brown siltstone and fine-grained, laminated sandstone
Diamictite with cobbles and boulders of dolomite, sandstone, quartz and black chert; sandstone matrix
Massive, poorly stratified sandstone with lenses and amygdales of clayey siltstone
Very coarse-grained diamictite with white, chert nodule bearing dolomitic blocks 40 to 100 cm across
LOCALSTRATI-GRAPHY
LITHOLOGY and COMMENTSARABIAN PLATE
SEQUENCESTRATIGRAPHY
Al Khlata Formation, Wadi Al Khlata, Oman
Al K
hlat
a F
orm
atio
n
UpperProterozoic
Khufai Formation
late
Wes
tpha
lian
(Mos
covi
an)-
Sak
mar
ian
Car
boni
fero
us-L
ower
Per
mia
n
PAL
AE
OZ
OIC
60
50
40
30
20
10
0 m pre-Khlata unconformity
AP1
AP5
Arabian PlateGlaciation 3
(AP G3) deposits
Figure 3: The Al Khlata Formation outcrops in Wadi Al Khlata in Oman (57o25’46”E, 19o46’43”N), whereit is about 100 m thick (Besems and Schuurman, 1987; Hughes Clark, 1988). The measured section isafter Platel et al. (1992). The Al Khlata Formation overlies the upper Proterozoic Khufai Formation ofthe Nafun Group, Huqf Supergroup. See Figure 1 for location of Wadi Al Khlata.
Angiolini et al., 2004
154
Figure 4: Stratigraphy of the Saiwan and redefined Gharif formations in the Khaluf map area, Oman(modified after Dubreuilh et al., 1992). The Saiwan Formation contains Lower Permian SakmarianMaximum Flooding Surface MFS P10 in Depositional Sequence DS P10. The supra-Saiwan unconformityextends across south and east Oman. The type section outcrop is near the Saiwan-1 well (see Figure 1),and is defined between 20o52’04”N, 57 o36’27”E, and 20 o52’26”N, 57 o36’26”E (Angiolini et al., 2003a).
LOCALSTRATIGRAPHY LITHOLOGY and COMMENTS
ARABIAN PLATESEQUENCE
STRATIGRAPHY
Saiwan type section and redefined Gharif formations, Khaluf map area, Oman
rede
fined
Gha
rif F
orm
atio
n
PE
RM
IAN
MID
DLE
Roa
dian
-Wor
dian
LOW
ER
Sak
mar
ian-
Kun
guria
n
PAL
AE
OZ
OIC
uppe
r un
itlo
wer
uni
tS
aiw
an F
orm
atio
n
Al KhlataFm
KhuffFm
Interbedded platy, grey limestone with crinoids, bivalves and brachiopods, and grey marl
Interbedded sandy shale and brown sandstone
Red sandy shale
Grey-white, coarse-grained, cross-bedded sandstone with pebbly beds, containing silicified wood
Channelized, matrix-supported conglomerate
Interbedded coarse-grained, cross-bedded sandstone with grey conglomeratic beds and green silty shale with marbling
Green shale with red marbling
White sandstone
Grey shale with red marbling
Red sandstone with silicified woodPachycyrtella omanensis
Diamictite with large boulders of crystalline rocks
Interbedded hard brown cross-bedded sandstone with brachiopods, bivalves and abundant crinoids, and yellow sandy marl
Green shale
Interbedded yellow sandstone, fine-grained argillaceous sandstone, green shale and bioclastic limestone containing abundant crinoids, large brachiopods, bryozoans and Bellerophon
"Met
aleg
ocer
as li
mes
tone
""B
elle
roph
onlim
esto
ne"
0 m
10
20
30
40
50
60
70
80
90
100
110
120 pre-Khuff unconformity
supra-Saiwan unconformity
DS P17
DS P15
DS P13
DS P10
AP G3pre-Saiwan unconformity
MFS P10284 Ma
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
155
The Saiwan Formation comprises two bioclastic units: the lower ‘Bellerophon Limestone’ (10-18 m, 33-59 ft thick), and the upper ‘Metalegoceras Limestone’ (35-40 m, 115-131 ft thick). Dubreuilh et al. (1992)indicate that in the kilometre-sized domal structures around the Saiwan-1 well (57o39’43”E, 20o54’00”N;2.5 km west of the Saiwan airstrip, Figure 1), the continental siliciclastic sedimentary rocks of theredefined Gharif Formation unconformably overlie the Saiwan Formation.
The Saiwan Formation was adopted by many authors (e.g. BRGM, 1992; Béchennec et al., 1993; LeMétour et al., 1995; Broutin et al., 1995; Angiolini et al., 1997, 2001, 2003a), and corresponds, in part, tothe Lower Gharif Member (Osterloff et al., 2004b). The unpublished type section in outcrop of theLower Gharif Member is located in the western Huqf region (57o22’55”E, 19o48’26”N) and northern Huqfregions (57o37’29”E, 20o50’45”N), and is 200 m (656 ft) thick in composite section (Hughes Clarke, 1988).
The Saiwan Formation was mapped as part of the Haushi Group sensu BRGM in three geological mapareas at 1:250,000 scale in Oman (BRGM, 1992), shown in Figure 1. In the southeast of the Mafraq maparea, the limited exposures of the Al Khlata and Saiwan formations in folded and faulted structures,makes it necessary to combine the Al Khlata and Saiwan formations in the 1:250,000 scale maps, into asingle undifferentiated unit (CPak-swn), even though they are quite easily distinguished on the ground.
The type section of the Saiwan Formation occurs in outcrop near the Saiwan-1 well in the Khaluf area(Figures 1 and 4; Dubreuilh et al., 1992), and is defined between 20o52’04”N, 57o36’27”E, and 20o52’26”N,57 o36’26”E (Angiolini et al., 2003a). In its type section, the formation attains a thickness of 50 m (164 ft)and the boundaries with overlying and underlying units are exposed. In the Duqm and Madraca areas(Platel et al., 1992), the Saiwan Formation is 20-40 m (66-131 ft) thick (Photo 1). In the Mafraq area(Figure 5; Roger et al., 1992), the Saiwan Formation is probably some 50 m (164 ft) thick, as in the type-section, although poor exposure make this difficult to ascertain.
In the Mafraq area, the Saiwan Formation consists of two separate units (Roger et al., 1992; Angiolini etal., 2001, 2003a) that are similar to the type section (Figure 4).
Photo 1: The Saiwan Formation outcrops in Jebel Gharif of Oman. Bioclastic hybrid limestones showstrong laminations; among the bioclasts, brachiopods are dominant. (Photo by Lucia Angiolini)
Photo 1
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156
The two units of the Saiwan Formation are described as follows: Saiwan lower unit ‘BellerophonLimestone’: about 5-10 m (16-33 ft) thick, consists of rusty-brown, cross-bedded quartz sandstonecontaining brachiopods, cephalopods, bivalves, gastropods, bryozoans, conularids and crinoids. Thesandstone beds are 1-2 m (3-7 ft) thick, and include rounded quartz and granite pebbles reworked fromthe Al Khlata Formation, interbedded with several layers of green silty-claystone. The lowermost 40-60cm of the Saiwan lower unit consist of cross-laminated bioclastic sandstone, named the Pachycyrtellabed (Angiolini et al., 2003a) (Photos 2-3). It contains silicified fossil wood as well as large spiriferinidbrachiopods.
Figure 5: The section of the Saiwan Formation in the Mafraq map area in Oman(modified after Roger et al., 1992).
MFS P10284 Ma
LOCALSTRATIGRAPHY LITHOLOGY and COMMENTS
ARABIAN PLATESEQUENCE
STRATIGRAPHY
Saiwan and redefined Gharif formations, Mafraq map area, Oman
rede
fined
Gha
rif F
orm
atio
nS
aiw
an F
orm
atio
nK
huff
Fm
Al K
hlat
aF
m
Bioclastic limestone
Sandy limestone tocalcareous sandstone
Bioclastic marl
ClaystoneSandy claystoneto siltstone
Sandstone
Conglomeratic lag
Diamictite
Plant remains(silicified wood)
Brachiopods
Crinoids
Bivalves
Coal flakes
Burrows
Ammonoids andNautiloids
Ripple marks
Cross-bedding
120
100
80
60
40
20
0 m
Alternating, cross-bedded, coarse- to medium-grained whitish sandstone with gravel lenses and silicified fossil logs, and red or green silty claystone.
Inter-bedded, cross-bedded sandstone, sandy claystone and highly bioclastic sandy limestone with bivalves, gastropods, brachiopods, crinoids, and bryozoans.
supra-Saiwan unconformity
pre-Saiwan unconformity
Grey bioclasticlimestone andmarl
Transitionalboundary
LEGEND(Figures 5 and 6)
DS P10
DS P13
DS P17
DS P15
AP G3
PE
RM
IAN
MID
DLE
Roa
dian
-Wor
dian
LOW
ER
Sak
mar
ian-
Kun
guria
n
PAL
AE
OZ
OIC
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
157
Photo 3: Detail of the Pachycyrtella bed at the base of the Saiwan Formation (Figure 4), showing thecharacteristic large spiriferinids which colonised, during the Sakmarian time, the shallow marineenvironments at the end of the Gondwanan deglaciation. (Photo by Lucia Angiolini)
Photo 2: The base of the Saiwan Formation in Saiwan area of Oman showing cross-laminated bioclasticsandstones of the Pachycyrtella bed (see Figure 4). (Photo by Lucia Angiolini)
Photo 2
Photo 3
Angiolini et al., 2004
158
Saiwan upper unit ‘Metalegoceras Limestone’: about 40 m (131 ft) thick, is made up of beds of alternatingcross-bedded calcarenitic sandstone and laminated sandy calcarenite, bioclastic limestone and marlstone.The sandstones are yellow-brown to white, in units several metres thick (2-6 m; 7-20 ft), commonlycoarse-grained and cross-bedded. The deposits are coarse- to fine-grained and contain a mixture ofquartz, feldspar and lithoclastic grains. These units are intercalated with highly fossiliferous limestonebeds about 10-30 cm thick along with subordinate micaceous green shale. They include an abundant,fragmented and highly diverse macrofauna of brachiopods, cephalopods, bivalves, gastropods, corals,conularids, ostracods, crinoids and trilobites, recording a significant increase of biodiversity.
Depositional Environment and Sequence Stratigraphy
The Saiwan Formation represents the first post-glacial Permian transgression (BRGM, 1992), the marginof which flooded the western part of the Haushi-Huqf palaeohigh. The shallow-marine deposits(shoreface) of this formation are characteristic of a high-energy environment. During this period, stronginfluxes of terrigenous material were derived from the emergent Haushi-Huqf Uplift.
Sharland et al. (2001) picked Arabian Plate Maximum Flooding Surface MFS P10 within bioturbatedshales immediately below the ‘Haushi Limestone’ within the Lower Gharif Member (Saiwan Formation).The maximum flooding surface is recorded by bioclastic sandstone located about five metres above thebase of the formation in the Saiwan type-section (Figure 5).
Fossils and Age
The very rich faunal content of the Saiwan Formation includes brachiopods, bivalves, gastropods,conularids, bryozoans, crinoids, barnacles, ostracods, fishes, asterozoans, trilobites, corals, nautiloidsand few ammonoids. The significant biodiversity coupled with the spectacular preservation of themacrofossils make them the object of numerous palaeontological studies since the fifties (Miller andFurnish, 1957; Hudson and Sudbury, 1959; BRGM, 1992; Angiolini et al., 1997, 2001; Jell and Willink,1993), besides those provided by Petroleum Development Oman.
Brachiopods dominate the fossil associations throughout the formation (Photo 4); only in its upperpart articulate crinoids and molluscs are locally very abundant. Based on the Unitary Association methodof Guex (1991), two brachiopod biozones have been established by Angiolini et al. (1997, 2003a): (1)Pachycyrtella omanensis Zone at the base of the formation; and (2) Reedoconcha permixta-Punctocyrtellaspinosa Zone immediately above. The basal Pachycyrtella Bed yields Pachycyrtella omanensis Angiolini,2001 associated with usually subordinate specimens of Strophalosia sp., bivalves (Cypricardinia? aff.elegantula, Myalinella sp., Nuculopsis cf. bangarraensis, Aviculopectinidae gen. et sp. indeterminate),gastropods, conularids, crinoids, bryozoans and barnacles. A few metres above, the brachiopodassemblage abruptly changes, recording a higher taxonomic diversity with the brachiopods Derbyiaharoubi Angiolini, 1997, Arctitreta cf bioni (Reed, 1932), Reedoconcha permixta (Reed, 1932) Neospirifer aff.hardmani (Foord, 1890), Neospirifer sp., Trigonotreta sp., Subansiria sp., Punctocyrtella spinosa Plodowski,1968, Cyrtella sp., Punctospirifer sp., Callispirina sp., Fletcherithyris sp., and ?Gilledia sp. (Reedoconchapermixta-Punctocyrtella spinosa Zone) associated with bivalves, gastropods, crinoids, conularids, rareammonoids (Metalegoceras hudsoni) and nautiloids. At the top of the Saiwan Formation, the taxonomicdiversity decreases again, the fossiliferous content chiefly consisting of Neospirifer, bivalves, gastropodsand spectacular articulated crinoids (Texacrinus sp.).
BRGM (1992) reported the following list of molluscs from the Saiwan lower unit (‘BellerophonLimestone’): Bellerophon cf., triangularis, Bellerophon spp., Bembexia sp., Murchisonia sp., Procrassatellaamarassiensis, Pseudomonotis sp., Schizodus sp., Stutchburia pallasi sp., and Nucula sp. Accordingly, theupper part of the Saiwan Formation (‘Metalegoceras Limestone’) is endowed with a comparablemolluscan fauna but is characterised by very abundant crinoid parts and a slightly different brachiopodassociation, and more common occurrence of ammonoids (Metalegoceras hudsoni) and orthoconicnautiloids. An ostracod association occurs in some of the shaley horizons with Hollinella emaciata,Roundyella aff. simplicissima, Monoceratina cf. parvula and Cavelinella nebrascensis.
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Photo 4: Lower Permian, Sakmarian brachiopods of the Saiwan Formation. (Photos by Lucia Angiolini)(1) Pachycyrtella omanensis Angiolini, 2001; dorsal view of an articulated specimen (natural scale).(2) Pachycyrtella omanensis Angiolini, 2001; dorsal valve showing barnacles borings (natural scale).(3) Pachycyrtella omanensis Angiolini, 2001; ventral valve bearing an attached specimen of Strophalosia sp.(4) Pachycyrtella omanensis (Angiolini, 2001), several articulated specimens with variable orientation.(5)Trigonotreta sp. dorsal valve (magnification x2.6)(6) Callispirina sp. ventral valve (magnification x2.6).
1 2
34
65
Photo 4
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In addition, the following fauna is mentioned in published literature, along with that provided byPetroleum Development Oman: bryozoans Fenestella sp., Leiocloma cf. globosa; brachiopods Spiriferellinasp., Dielasma sp., Asyrinx haushiensis (=Pachycyrtella omanensis); gastropods Meekospira sp., Soleniscus(Strobeus) mucronatus; bivalves Astartella permocarbonica, Myalina sp., Nucula sp., Procrassatellaamarassiensis, Pseudomonotis sp., Schizodus sp., Stuchburia pallasi; cephalopods Eoasianites sp.;pseudorthoceratids; various orthocones; the nautiloid Gzheloceras uralense; the trilobite Pseudophillipsialipara and the ostracod Roundyella aff. simplicissima.
According to Miller and Furnish (1957), this fossil fauna indicates that the Saiwan Formation is of EarlyPermian, Sakmarian-Artinskian age; whereas Hudson and Sudbury (1959) indicate a Sakmarian agefor the formation.
Angiolini et al. (1997, 2001, 2003a) identified Pachycyrtella omanensis in the basal Pachycyrtella Bed of theSaiwan Formation which is associated with a smaller number of specimens of the genus Strophalosia.The latter genus straddles the early-late Sakmarian boundary, and they therefore attributed a mid-Sakmarian age for the base of the Saiwan Formation. They add that brachiopod, ammonoid and bivalveassemblages in the main part of the Saiwan indicate a late Sakmarian age, as documented by theoccurrence of genera such as Arctitreta, Punctocyrtella, Subansiria, Fletcherithyris and species of Reedoconcha,Trigonotreta and Neospirifer, all belonging to the Reedoconcha permixta-Punctocyrtella spinosa Zone. This issupported by correlation with the western and eastern Australian Permian biostratigraphic zonations(Archbold, 1998; Briggs, 1998). According to Love (1994), Stephenson and Osterloff (2002), andStephenson et al. (2003) the subsurface Lower Gharif Member is Artinskian based on palynologicalevidence.
Sharland et al. (2001) follow the age interpretation of Angiolini et al. (1997, 2001) and consider MFS P10as late Sakmarian with an age of about 272 Ma according to the scale of Gradstein and Ogg (1996).Based on the latest Permian age calibrations (Jin et al., 1997; Menning et al., 1997; Menning, 2001a,b;International Commission Stratigraphy website, 2002) the Sakmarian spans the period 287-280.3 Ma, suchthat if MFS P10 is indeed late Sakmarian, then it should be dated at about 284 Ma (rather than 272 Ma).
REDEFINED GHARIF FORMATION
Lithostratigraphy
The redefined Gharif Formation of BRGM (1992) corresponds in part to the subsurface Middle andUpper Gharif members (Hughes Clarke, 1988; Guit et al., 1985; Osterloff et al., 2004b). It comprises thedeposits that lie unconformably above the Saiwan (Lower Gharif Member or Haushi Limestone) or AlKhlata formations, and conformably below the first marine deposits of the Khuff Formation. Theredefined Gharif Formation is mapped in the Mafraq, Khaluf, and Duqm-Madraca areas (BRGM, 1992).It is some 70-100 m (230-328 ft) thick at outcrop in the Haushi area (Figures 4-6). The Middle andLower Gharif members are proposed as Depositional Sequences DS P13 and DS P15 (Osterloff et al.,2004b). Near the Saiwan-1 well (Figures 1 and 4) and in the western Saiwan area, the formation consistsof two units (BRGM, 1992).
Redefined Gharif Formation, lower unit
This unit is 30-40 m (98-131 ft) thick, and consists of mottled shale layers, intercalated with severalmetre-thick beds of white, cross-bedded sandstone. The sandstone is typically coarse-grained andincludes lenses of fine conglomerate with rounded centimetre-sized clasts, plus fragments of silicifiedfossil wood in some beds. The finer-grained layers grade from claystone to siltstone and are grey-greento brick-red in color. It seems probable that the outcropping redefined Gharif lower unit is equivalentto the subsurface Middle Gharif Member subunit 3 (Osterloff et al., 2004b).
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
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Redefined Gharif Formation, upper unit
The upper unit is some 30-35 m (98-115 ft) thick, and consists of white-grey to locally brown, generallycoarse-grained, cross-bedded sandstone. It contains conglomerate lenses with rounded polygeneticclasts of mainly quartz and granite, and typically includes fossil wood, determined to include theginkgophyte Baieroxylon cf. implexum. The sandstone sequences are broadly upward-fining and thinning,and terminated by commonly lenticular, green or red-mottled shale. This becomes more common and
LOCALSTRATIGRAPHY LITHOLOGY and COMMENTS
ARABIAN PLATESEQUENCE
STRATIGRAPHY
Redefined Gharif and Khuff formations, Haushi region, Mafraq map area, Oman
TRIASSICMinjur Formation
Khu
ff F
orm
atio
nre
defin
ed G
harif
For
mat
ion
80
70
60
50
40
30
20
10
0 m
Varicolored claystone and sandstone with ferruginous crust
Interbedded grey bioclastic limestone, calcarenite and bioclastic marl
Bioclastic sandstone
Alternating sandstone with coal flakes and pyritic shale
Alternating cross-bedded coarse- to medium-grained whitish to reddish sandstone with gravel lenses, silicified fossil logs and red or green silty claystone
DS P17
AP6
AP5
DS P15
DS P13
PAL
AE
OZ
OIC
PE
RM
IAN
MID
DLE
Roa
dian
-Wor
dian
pre-Minjur unconformity
Figure 6: Lithostratigraphy of the redefined Gharif and Khuff formations in Mafraq map area, Oman(modified after Roger et al., 1992) shows the base of the marine Khuff Formation is picked at the base ofthe bioclastic sandstone (Khuff unit C in Figures 7 and 8). The sequence boundary, however, may occursome 15 m lower at the top of Depositional Sequence P15 (base Gharif subunit B in Figures 7 and 8).
Angiolini et al., 2004
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Figure 7: The top sequence boundary of Depositional Sequence Permian 15 (DS P15) in the Haushioutcrop is picked at the base of the Upper Gharif subunit B (Crumeyrolle et al., 1997; Angiolini et al.,2001). Subunit B (also red beds) corresponds to the ‘middle unit’ of Broutin et al. (1995) and representsan estuarine meandering channel complex as shown in the Northern Cliff (Figure 8).
LITHOLOGYLOCAL STRATIGRAPHY ENVIRONMENTSEQUENCE
STRATIGRAPHY
low
er
subu
nit A
uppe
r G
harif
san
dsto
ne
basa
l uni
t
red
beds
red
beds
mid
dle
unit
uppe
r un
it
subu
nit B
Mem
ber
1M
embe
r 2
MID
DLE
Roa
dian
rede
fined
Gha
rif F
orm
atio
n
Wor
dian K
huff
For
mat
ion
Bro
utin
et a
l.(1
995)
Cru
mey
rolle
et
al.
(199
7);
Ang
iolin
i et a
l. (2
001)
Mar
ine
faun
a
CoastalPlain
Fluvial
Marine
AP6
AP5
PAL
AE
OZ
OIC
PE
RM
IAN
SequenceBoundary
Cla
ysto
ne
Silt
ston
e/M
arl
Fin
e sa
ndst
one
Med
. san
dsto
ne
Coa
rse
sand
ston
e
Con
glom
erat
e
50 m
Boundary of Gharif and Khuff formations, Huqf, Oman
C
D
DEPOSITIONALSEQUENCE P15
DEPOSITIONALSEQUENCE P17
mfs
Gha
rifpa
laeo
flora
Con
tinen
tal f
lora
Muscat
Arabian Sea
Gulf of Oman
OMAN
SAUDIARABIA
UAE23°
21°
19°
585654
21
19
23
54 56 58 60
0 150
km
NorthCliff
Hau
shi-H
uqf U
plift
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
163
more silty or sandy through the top 15 m (49 ft) of the formation, immediately beneath the lowestfossiliferous beds of the Khuff Formation. The uppermost few metres consist of thinly-interbedded,dark grey carbonaceous shale and gritty sandstone lenses.
Located east of the Haushi anticline (Figures 1, 7 and 8), in the ‘Northern Cliff’ (about 20-30 m or 67-100ft high; 21o00’34” N, 57 o39’35” E and 21 o02’09” N, 57 o42’22” E), the redefined Gharif upper unit hasbeen further subdivided into subunits A and B (Figures 7 and 8; Broutin et al., 1995; Crumeyrolle et al.,1997; Razin and Platel, 1998; and Angiolini et al., 2001).
Redefined Gharif upper unit, subunit A has a maximum exposure of 50 m (164 ft) in the NorthernCliff, and consists of plurimetre-thick, fining-upward sequences. It comprises channel bodies of coarse-grained sandstone, showing festoon cross-bedding, interbedded in variegated silt clays. Red palaeosolhorizons with numerous root traces occur between the sequences and indicate prolonged periods ofemersion. The sandstone occurs as single or multi-storey channels locally showing erosive scours. Thebase of each sand body is sharp and erosive, and shows very coarse to pebbly sand with large-scaletrough cross-bedding.
Redefined Gharif upper unit, subunit B is about 1-15 m (3.3-49 ft) thick and overlies subunit A alongan irregular surface showing incised channels up to 10 m deep (33 ft) deep (Figure 8).
Osterloff et al. (2004b) consider the outcropping redefined Gharif upper unit to correspond to the UpperGharif Member of subsurface. In particular, subunit B may correspond to the subsurface uppermostCycle 8 of the Upper Gharif Member, beneath the main Khuff transgressive unit.
Figure 8: The top sequence boundary of Depositional Sequence P15 is interpreted in the Northern Cliff,east of the Haushi structure (Crumeyrolle et al., 1997). The sequence boundary (red) is placed at theunconformity below the estuarine meandering channel complex (subunit B) that cuts into the UpperGharif braided fluvial channel sand sheet (subunit A).
Gharif and Khuff formations, Haushi Northern Cliff, Oman
Shallow marine carbonates and clastics
Transgressive shoal/barrier clastics
Braided fluvial channel sand sheet
Khuff Formation
unit D
unit C
estuarine meandering channel complex
10 m
1 2 km
subunit BRedbeds
subunit Aor basal
unitupper Gharif Formation
Southwest Northeast
Angiolini et al., 2004
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Depositional Environment and Sequence Stratigraphy
The depositional environment of the redefined Gharif lower unit is characterised as floodplain and/orephemeral shallow-lake environments as indicated by clayey sand flats with the development ofpalaeosols and overbank and/or minor sand channels (e.g. Angiolini et al., 2001). The interbeddedsandstones are in places bioturbated indicating over bank deposits within a flood plain and/orsubaqueous environment. Current directions are to the north and to 100o N.
Angiolini et al. (2001) add that some sections show cosets of 2-D and 3-D megaripples and ripples;however, their paucity suggests deposition did not occur in a large water body. These sandstone bodiesare sheet-like deposits with no discernible lateral or downstream accretion. Restricted areas of cross-bedding are separated by wider zones of tabular sets which possibly define areas of more persistentchannel flow and areas of sand flat in the inferred braid plain. These overlie a floodplain facies withmud cracks and palaeosols.
In the south Mafraq and north Khaluf map areas, the redefined Gharif lower unit gradually disappearsso that in places the redefined Gharif upper unit rests directly on the Al Khlata Formation (BRGM,1992). This pattern indicates progressive onlap across the Haushi-Huqf Uplift. In south Mafraq, thesandstone beds reach a cumulative thickness of some 15 m (49 ft) and consist of cross-bedded, coarse-grained sandstone, containing lenses of gravel, silicified wood fragments and large seeds (Gharif subunitA). The sandstone beds have a well-defined channel form marked by oblique bedding related to thelateral migration of point bars. The channels cut into predominantly red-coloured claystones of afloodplain facies (Gharif lower unit).
The sandstone bodies of the redefined Gharif upper unit, subunit A (BRGM, 1992; Angiolini et al.,2001) form extensive channel belts interpreted as sandy sheets of broad braided to low-sinuosity riversystems. Large-scale accretion surfaces and low-angle dipping surfaces in a down-current directionare seen locally in massive, coarse-grained facies that are interpreted as longitudinal or transversealluvial bar deposits. The depositional environment is interpreted as an alluvial floodplain.
The uppermost subunit B of the redefined Gharif upper unit is made up of three types of interbeddedfacies:
Subunit B, facies 1 is composed of coarse to very coarse sandy lenticular bodies developed along largelow-angle dipping surfaces. Bi-directional cross-bedding along the main accretion surfaces, as well asnumerous clay chips and drapes, indicate that flood tidal currents were active.
Subunit B, facies 2 consists of heterolithic sandstone-claystone bodies, some 100 to 1,000 m in width,characterised by large inclined cross-stratifications; these heterolithic facies are made up of coarse- tofine-grained, sheet like, graded, sandstone sets varying in thickness from a decimetre to severaldecimetres, interbedded with dark to variegated laminated silty claystone with scattered plant debris. Theseare interpreted as coastal plain deposits associated with distribution channels filling vast incised valleys.
Subunit B, facies 3 is a dark laminated silty shale with subordinate interbeds of medium to fine-grainedsandstone lenses. These deposits are considered as swamp claystones with very rich organicaccumulations made up of plant debris and pollen.
Angiolini et al. (2001) consider Upper Gharif subunit B deposits as representing a system of coalescentestuarine meander bars filling a vast incised valley. The occurrence of cyclic beds with climbing ripples,and upper flow regimes parallel laminations, suggests fluvial, flood-dominant regime periods duringpoint bar migration. The occurrence of episodic mud flasers and drapes, sigmoidal cross-bedding andbi-directional cross-bedding, also suggests some tidal influence. Periods of weak fluvial discharge, followedby abandonment, correspond to the infill of organic shales within laterally juxtaposed clayey marshes.
Fossils and Age
The age of the redefined Gharif lower unit is not well constrained because of poor fossil remains(Angiolini et al., 2001). Silicified tree trunks, in places several metres long, are common in the redefined
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
165
Gharif Formation. Subunit B of the uppermost Gharif Formation contains a rich macroflora (Gondwanantaxas as Glossopteris, Cathaysian taxas as Gigantopteris, Euramerian taxas as Otovia (Walchia) hypnoides),and microfloral assemblage including numerous spores and monosaccate, non striate and striatebisaccate pollen grains (Broutin et al., 1995; Angiolini et al., 2001). This flora is not diagnostic of aprecise age, but considered by these authors as ?Roadian-?early Wordian. According to P. Osterloff(2003, written communication) the sandstone bodies of the redefined Gharif upper subunit in outcropmay most likely be ?Kungurian-?Roadian and as young as Kazanian (Roadian-early Wordian).
The following taxa were determined by J. Broutin (1995):
Trilete spores: Laevigatosporites vulgaris, Leiotriletes spp., Retusotriletes cf. simplex, Calamaspora spp.,Verrucosisporites sp., Cyclogranisporites arenosus, Polypodiisporites cf. mutabilis, Cristatisporites sp., Brazileasp., Chordecystia sp.
Monosaccate pollen: Florinites pellucidus, F. eremus, Potonieisporites novicus, Potonieisporites sp.,Playfordiaspora cancellosa, Scheuringipollenites ovatus, Scheuringipollenites spp.
Not-striate bisaccate pollen: Vitreisporites pallidus, Vesicaspora schemeli, Falcisporites sp., Gardenasporitessp., Cedripites priscus, Platysaccus sp.
Striate bisaccate pollen: Protohaploxypinus amplus, P. devinensis, P. hartii, P. limpidus, P. microcorpus, P.pennulatus, P. perfectus, Lunatisporites cf. pellucidus, Lunatisporites sp., Lueckisporites singhii, L. virkkiae,Corisaccites alutas, Striatoabietites multistriatus, S. richteri, Striatopodocarpites cancellatus, S. fusus,Weylandites lucifer.
KHUFF FORMATION
Lithostratigraphy
The Khuff Formation (Steineke et al., 1958; Angiolini et al., 2001, 2003a,b; Osterloff et al., 2004b) is bestexposed in the homoclinal western flank of the anticlinorium, from the east of the Haushi fold beltnorthwards as far as Jebel Tharay (southwest of Saiwan). The Khuff Formation corresponds to the‘Lusaba Limestone’ (Goldring, 1957; Miller and Furnish, 1957; Morton, 1959; Hudson and Sudbury,1959), and is mapped in the Haushi-Huqf region by BRGM authors (Dubreuilh et al., 1992; Platel et al.,1992; Roger et al., 1992).
Photo 5: The Jurf, Khuff and Gharif formations outcrop in Jebel Gharif of Oman (see Figure 11). Thegrey limestones and marlstones of the Khuff Formation unconformably overlie the red sandstones ofthe Gharif Formation and are, in turn, sharply truncated by the dolostones of the Cretaceous JurfFormation. Height of the cliff is about 50 metres. (Photo by Lucia Angiolini)
Photo 5
Jurf Formation
Khuff Formation
Gharif Formation
Angiolini et al., 2004
166
G. g
hab
aens
is-K
. tes
coru
m Z
one
Acr
itosi
a sp
.-G
lob
osob
ucin
a Z
one
N. (
N.)
arab
icus
-C. m
anar
olla
i Zon
e
mem
ber
3m
embe
r 2
mem
ber
2m
embe
r 1
Sub
unit
BU
nit C
Khu
ff F
orm
atio
n
Khu
ff F
orm
atio
nre
defin
ed G
harif
Fm
Uni
t D
Maximumflooding surface
marineflooding surface
1 m
1 m
Ammonites
Bivalves
ConodontsCorals
Crinoids
Brachiopods
Fish
Gastropods
Scaphopod
Nautiloid
Bryozoa
Trilobites
Redefined Gharif and Khuff formations, Oman
Bioturbatedsandstone
Cross-laminatedsandstone
Marlstone
Marlstone
Marlstone
Mudstone
Mudstone
Mudstone
Bioclasticlimestone
Bio-intraclasticlimestone
Sandylimestone
Limestone
Bioclasticsandstone
Ostracod
Figure 9
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
167
The Khuff Formation lies everywhere conformably on the Gharif Formation. The base is picked at thefirst calcareous bed immediately beneath the marine marl, containing bivalve and brachiopod debris(Figures 5-10). This bed overlies the continental deposits of grey, sandy shale with sandstone lenses, atthe top of the Gharif Formation (Figures 7 and 8).
In the Khaluf and Mafraq areas, the top of the Khuff Formation is an unconformity with continentalalteration where rapid emersion and in situ brecciation took place. The uppermost Khuff carbonate-marl layers are normally reddened, indicative of subaerial weathering, and are abruptly overlain byvariegated, red shale and sandstone of the Triassic Minjur Formation. In the southwestern Duqm andMadraca areas (Figure 11, Platel et al., 1992), deep erosion after a period of deformation has completelyremoved the Jurassic Sahtan Group. Throughout this area, the yellow dolomitic limestone of theCretaceous Jurf Formation (Thamama Group) unconformably overlies the dark grey flags of the KhuffFormation (Photo 5).
In the Haushi-Huqf area, the Khuff Formation is about 30 m (98 ft) thick (Photos 6 and 7). It comprisessequences, several metres thick, of grey marl showing worm tubes and well-preserved fossils withinterbeds (about 10 cm thick) of granular, grey to yellow-brown limestone, rich in large fossil remains.At the base, the first few metres consist of limestone beds that contain a fine-grained sandy fraction(Photo 8). Higher in the formation, yellow calcarenite beds appear; while the most common type oflimestone, forming the tops of sequences, consists of biomicritic wackestone followed by highly
Photo 6: The Khuff Formation members 1-3 outcrop in the Haushi Northern Cliff of Oman (see Figures7-9). The three Khuff members are easily distinguished by their sharp lithological contrast. Member 2chiefly consists of marls and shows a very low topographic relief; its base marks a flooding surface.Height of the cliff is about 30 metres. (Photo by Lucia Angiolini)
Figure 9 (facing page): Stratigraphy of the redefined Gharif and Khuff formations, Haushi region(modified after Angiolini et al., 2001). The lower sequence boundary of the Middle Permian transgressionis placed below Gharif subunit B. The flora in subunit B is not diagnostic of a precise age, but considered?Roadian-?early Wordian. The marine fauna of the exposed lower Khuff Formation support a MiddlePermian Wordian age. Foraminifera confirm a Middle Permian age (Wordian and Capitanian). Conodontfauna from Khuff member 3 suggests a late Wordian age.
Photo 6
Khuff Formationmember 3
Khuff Fmmember 2
Khuff Fmmember 1
Gharif FormationGharif Formation
Angiolini et al., 2004
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Photo 8: Khuff Formation members 1 and 2 in the Haushi Northern Cliff in Oman seen along thesection drawn in Figure 9. Height of the cliff is about 12 metres. (Photo by Lucia Angiolini)
Photo 7: Khuff Formation members 1-3 outcrop in the Haushi Northern Cliff in Oman (see Figures 7-9).Khuff member 1 marks the passage of the foreshore facies of the basal Khuff Formation. Khuff members2 and 3 were deposited in a carbonate shelf. Height of the cliff is about 20-25 metres. (Photo by LuciaAngiolini)
Khuff Formationmember 3
Khuff Formationmember 2
Khuff Formationmember 1
Gharif Formation
mbr
3 K
huff
Fm
mbr
2m
br 1
Photo 7
Khuff Formationmember 2
Khuff Formationmember 1
Photo 8
Saiwan, Gharif and Khuff formations, Haushi-Huqf Uplift, Oman
169
fossiliferous grainstone with well-preserved fossil fauna (condensed sequences). The end-of-sequencediscontinuities are commonly characterised by large-scale symmetrical ripple-marks indicative of high-energy conditions in the subtidal environment of deposition.
In the outcrop of this Mafraq Map area (Figure 6; Roger et al., 1992), the Khuff Formation is relativelythin, averaging around 20-30 m (66-98 ft) thick. The formation consists of grey-green, fossiliferous,marl interbedded with several decimetre-thick layers of highly bioclastic, argillaceous limestone. Aninflux of terrigenous material is visible in the first four metres (13 ft) of the formation, shown by thinbeds of quartzitic sandstone that alternate with white, ripple-marked argillaceous limestone. This levelencloses an abundant macrofauna of ammonoids, nautiloids, brachiopods, serpulids, etc. Above this,the coarse-grained fraction is replaced by grey-white to greenish-coloured marl. This succession formsrepeat-sequences that start with thick marl that becomes progressively burrowed, and end with adecimetre-thick resistant bed of ochre-coloured, bioclastic limestone.
The individual sequences become noticeably thinner (average thickness of 2 m/7 ft) in the topmost 10 m (33ft) of the formation, resulting in the section showing a relative increase in number of carbonate intervalsof a wackestone-packstone texture. The carbonate beds display large-scale symmetrical ripple marksformed by wave action; their upper surface is generally marked by a hard ground or the preferentialaccumulation of an abundant and diverse fauna including cephalopods, crinoids, bryozoans,brachiopods and asteroids. Most of the fauna occurs within this upper interval. The macrofauna ispreferentially concentrated within the packstone-textured carbonate intervals, and microfauna(ostracods) is also present.
Figure 10:Stratigraphy ofthe redefinedGharif and Khuffformations,Duqm andMadraca maparea (Platel et al.,1992).
Brecciated grey-beige limestone
Bioclastic limestone
Yellow marl and marly limestone
Alternating grey marl and marly limestone
Grey bioclastic limestone with brachiopods, bryozoans and molluscs
Green marl with white palustrine calcareous nodules
Yellow and white to purple argillaceous sandstone
Whitish argillaceous sandstone and green marbled shale
Palaeosol
Interbedded yellow to grey cross-bedded sandstone, yellow sand, whitish marl and bioclastic limestone with abundant brachiopods, bryozoans, echinoids and molluscs
LOCALSTRATI-GRAPHY
LITHOLOGY and COMMENTSARABIAN PLATE
SEQUENCESTRATIGRAPHY
Redefined Gharif and Khuff formations, Duqm and Madraca map area, Oman
rede
fined
Gha
rif F
mK
huff
For
mat
ion
Naq
d F
orm
atio
n
MIO
CE
NE
CE
NO
ZO
IC
PE
RM
IAN
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Depositional Environment and Sequence Stratigraphy
The Khuff Formation consists of shallow-water carbonate deposits laid down across the Arabian Platformduring the widespread transgression that started in the mid-Permian. The transgression covered thewestern edge of the Haushi-Huqf Uplift (Hughes Clarke, 1988). In the Northern Cliff, above subunit Bof the redefined Gharif Formation, the basal part of the Khuff Formation is characterised by members 1(units C, D), 2 and 3 (Angiolini et al., 2001, 2003b) (Figures 7-9; Photo 6). The lowermost Khuff unit Chas a sharp erosional contact with the underlying shale of Gharif subunit B.
Khuff member 1, unit C is about 2-4 m (6.6-13.2 ft) thick, and consists of stacked graded sequences,several decimetres thick, of coarse to fine-grained, laminated clayey sandstone and contains an increasingfraction of highly abraided marine bioclasts. These beds form a very tabular continuous horizon, andare considered fluvial-infuenced; the intense bioturbation of these facies is related to lagoonal or bayenvironments. Thin to medium sandstone beds with NNE-directed straight-crested wave ripples areintercalated at the base.
Khuff member 1, unit D, about 3 m (9.9 ft) thick and fossiliferous at the base (brachiopods, conodonts,crinoids, ostracods) (Photo 9), is made up of shallow marine yellowish to whitish carbonate mudstoneshowing interbedded rippled bioclastic sandy layers (Photo 10). Khuff units C and D mark the passageof the foreshore facies of the basal Khuff Formation.
Khuff member 2 is 12 m (39 ft) thick, and consists of burrowed marlstones and marly limestones,interbedded with thin sandy bioclastic tempestites (Photo 11). The upper part consists of bioclasticgrainstone beds in which wave ripples occur regularly. It lies conformably on unit D. Marlstones andlimestones are rich in ostracods.
Photo 9: Khuff Formation member 1 (upper part) in the Haushi Northern Cliff in Oman, showing avery rich bioclastic bed, full of the convex-up valves of the brachiopod Celebetes manarollai Angiolini,1999. (Photo by Andrea Tintori).
Photo 9
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Photo 10: Unit D of Khuff Formation member 1 in the Haushi Northern Cliff in Oman showing wave-rippled, sandy bioclastic bed along the section drawn in Figure 9. Height of the cliff is about 4 metres.(Photo by Lucia Angiolini)
Photo 11: Member 2 of the Khuff Formation in the Haushi Northern Cliff in Oman showing stronglyburrowed marlstones. (Photo by Lucia Angiolini)
Photo 10
Photo 11
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Khuff member 3 is 21 m (69 ft) thick, and ends the Khuff Formation with an erosional surface at its top,below the red siliciclastic continental deposits of the poorly constrained Triassic-Jurassic MinjurFormation (Photo 12). The major facies of this unit displays an inflection toward marly-carbonate micritewith cephalopods, brachiopods, ostracods, and conodonts (Roger et al., 1992; Broutin et al., 1995;Angiolini et al., 1998, 2003b; Angiolini and Bucher, 1999; Crasquin-Soleau et al., 1999; Crasquin-Soleau,2003). These facies exhibit interbedded grainstone layers with wave ripples that have been interpretedby Angiolini et al. (2001, 2003a, b) as tempestites, including mixed autochthonous and allochthonousfossils (algae, bivalves, brachiopods, conularids, crinoids, benthic foraminifera, gastropods, conularids,bryozoans, ostracodes). Vertebrate remains are also common, mostly represented by durofagous fishesfeeding on shallow-water molluscs. The interbedded marlstones, instead, contain chiefly infaunalbivalves and quasi-infaunal productids.
The transition from Gharif subunit B to the Khuff Formation is a trangressive trend; from base to top:(1) Gharif subunit B: distal fluviatile system bordering a coastal plain; (2) Khuff member 1, units C and D:clastic transgressive shoal/barrier; and (3) Khuff members 2 and 3: carbonate platform. The lowersequence boundary of the transgression is interpreted at the base of subunit B (Broutin et al., 1995;Angiolini et al., 2001). It corresponds to a relative sea-level fall that resulted in fluvial incision (Figure8). They interpret Gharif subunit B, and Khuff units C and D as the TST and a marine flooding surface(mfs) at the base of member 2 of the Khuff Formation.
Grey micritic palustrine limestone with flint nodules
White micritic limestone, brecciated at base
White limestone with burrows
Brecciated rusty brown dolomite
Alternating yellow dolomitic limestone and dolomitic marl
Black silty shale
Grey palustrine limestone
Alternating marl and clay
Grey calcareous paleosol
Marl with bivalves
Grey cross-bedded sandstone with abundant molluscs (beach-rock)
Interbedded beige to grey laminated marl, rusty brown sandstone, and bioclastic limestone with corals and abundant bivalves
LOCALSTRATI-GRAPHY
LITHOLOGY and COMMENTSARABIAN PLATE
SEQUENCESTRATIGRAPHY
Khuff Formation, Duqm and Madraca map area, Oman
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AP6
Figure 11: The top of theKhuff Formation in theDuqm and Madraca maparea is eroded by the pre-Jurf unconformity (afterPlatel et al., 1992).
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Photo 13: Ammonoids (Pseudohalorites arabicus Miller and Furnish 1957, determined by M. Balini inAngiolini et al., 2003b) in the upper part of member 2 of the Khuff Formation, Haushi Northern Cliff,Oman. Each specimen is about 15-20 mm in diametre. (Photo by Andrea Tintori)
Photo 12: Member 3 of the Khuff Formation in the Haushi Northern Cliff in Oman, showing bioclasticlimestones and biointraclastic limestones below the unconformable red beds of the Triassic-LowerJurassic Minjur Formation. Height of the cliff is about 7-8 metres. (Photo by Lucia Angiolini)
Photo 12
Khuff Formationmember 3
Minjur Formation
Photo 13
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Fossils and Age
The Khuff Formation is characterised by an abundant and diverse fauna, much of which is beautifullypreserved intact and unbroken, particularly within the marly intervals (BRGM, 1992). Even thoughbrachiopods, bivalves, gastropods and cephalopods predominate, the macrofauna also includesbryozoans, echinoderms, trilobites, corals, conularids and vertebrate remains. Foraminifers, algae andostracods are also present. An abundance of faunal material has been gathered, determined and
Photo 14
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published by Goldring (1957), Miller and Furnish (1957), Hudson and Sudbury (1959), Angiolini et al.(1998), Angiolini and Bucher (1999), Crasquin-Soleau et al. (1999), Crasquin-Soleau (2003), Dickins(1999), Angiolini et al. (2001, 2003b). A recent synthesis of most of the fauna has been undertaken byAngiolini et al. (2003b), who listed:
Cephalopods: Pseudohalorites arabicus Miller & Furnish, 1957, Stacheoceras sp., nautilocon nautiloids(Photo 13).
Brachiopods: Lingula sp., Perigeyerella raffaellae Angiolini, 1999, Derbyia cf. diversa Reed 1944, Neochonetes(Nongtaia) arabicus (Hudson and Sudbury, 1959), Celebetes manarollai Angiolini 1999, Haydenella sp.,Dyschrestia rugosa Angiolini 1999, Juresania omanensis Hudson and Sudbury 1959, Kozlowskia tescorum(Hudson and Sudbury, 1959), Bilotina yanagidai Angiolini 1999, Vediproductus sp. [= Calliprotonia sp. inAngiolini and Bucher (1999)], Linoproductus aff. kaseti Grant 1976, Magniplicatina sp., Grandaurispinaghabaensis Angiolini 1999, ?Cyclacantharia sp., Globosobucina sp., Acritosia sp., Edriosteges sp., ?Darlinuriasp., Orthotichia cf. bistriata Reed 1944, Terebratuloidea sp., Cleiothyridina cf. seriata Grant 1976, Squamulariasp., Martiniopsis sp., Spiriferellina sp., Callispirina sp., Hemiptychina sp., and Dielasma spp. (Photo 14).
Conodonts: Hindeodus wordensis Wardlaw, 2000, Merrillina praedivergens Kozur and Mostler 1976 andSweetina sp.
Ostracods: Acratia cf. subularis Gusseva 1972, Acratia n. sp.2, Acratia n. sp.3, Acratina diffusa Schneider1959, Bairdia cf. acrisa Stepanaitys 1975; Bairdia sp.1, Bairdia omanensis Crasquin-Soleau 1999, Birdsallela?spp., Carinaknightina braccinii Crasquin-Soleau 1999, Cavellina boomeri Crasquin-Soleau 1999, Cavellinan. sp.4, Cavellina gerryi Crasquin-Soleau 1999, Cavellina? huqfensis Crasquin-Soleau 1999, Fabalicyprisparva Wang 1978, Geffenina wangi Crasquin-Soleau 2003; Healdianella? n. spp. Crasquin-Soleau 1999,Hollinella (H.) benzartiae Crasquin-Soleau 1999, Hollinella (H.) herrickana Girty 1909, Hollinella (H.) martensiCrasquin-Soleau 1999, Jordanites lordi Crasquin-Soleau 1999, Kindella sp.1, Knightina cf. fildari Payne1937, Knightina unnoda Wang 1978, Langdaia hornei Crasquin-Soleau 1999, Moorites cf. minitus Warthin1930, Moorites cf. suboblonga Wang 1978, Perprimitia brevirostris Schneider 1958, Perprimitia sp., Placideacf. petschorensis Schneider 1958, Roundyella cf. bellatula Bradfield 1935, Roundyella suboblonga Wang 1978,Sargentina minuta Wang 1978, Sargentina transita Kozur 1985, Sargentina woutersi Crasquin-Soleau 1999,Sulcella arabica Crasquin-Soleau 1999, Sulcella sulcata Coryel & Sample 1932, Sulcella superpermiana Kozur1985 (Photo 15).
Vertebrates: Menaspoid scales, Cladodont teeth, Hybodont teeth and denticles, Deltodus teeth,Actinopterygian teeth, scales and vertebrae.
Foraminifera: Vachard in Angiolini et al. (1998) preliminarily identified some smaller foraminifera.An updated list (Photo 16) is as follows: Diplosphaerina ex gr. inaequalis (Derville, 1931), Earlandia ex gr.minor (Rauzer-Chernousova, 1948); Calcitornella sp., Multidiscus cf. arpaensis Pronina, 1988, Nodosaria
Photo 14 (facing page): Middle Permian, Wordian, brachiopods of the Khuff Formation. Scale asindicated. (Photo by Lucia Angiolini)(1) Derbyia cf. diversa Reed, 1944, ventral valve, x1.(2) Neochonetes (Nongtaia) arabicus (Hudson and Sudbury, 1959), ventral valve, x1.(3) Bilotina yanagidai Angiolini, 1999, interior of dorsal valve, x1.(4) Celebetes manarollai Angiolini, 1999, ventral view of an articulated specimen, x1.(5) Linoproductus aff. kaseti Grant, 1976, ventral valve, x1.(6) Juresania omanensis Hudson and Sudbury, 1959, articulated specimen with gastropods, x1.(7) Perigeyerella raffaellae Angiolini, 1999, two ventral valves with bivalves, x1.(8) Acritosia sp., articulated specimen, x1.(9) Juresania omanensis Hudson and Sudbury, 1959, ventral view of an articulated specimen, x1.(10) Vediproductus sp., ventral valve, x1.(11) “Dielasma” sp., ventral view of an articulated specimen, x1.(12) Magniplicatina sp., ventral valve, x1.(13) Globosobucina sp. , ventral valve with spines, x1.
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Photo 15: Examples of ostracod species of the Khuff Formation in Oman. Scale bar is 100 micrometre.(Photo by S. Crasquin-Soleau)(1-2) Langdaia hornei Crasquin-Soleau 1999; (1) holotype, left lateral view; (2) paratype right lateral
view.(3) Carinaknightina braccinii Crasquin-Soleau 1999; holotype, left lateral view, x 45, MGL74654, sample
A18A.(4) Knightina cf. fildari Payne 1937 sensu Crasquin-Soleau and Orchard 1994; left lateral view.(5) Knightina unnoda (Wang 1978); left lateral view.(6-7) Hollinella (H.) benzartiae Crasquin-Soleau 1999; (6) holotype, right lateral view; (7) right lateral
view.(8-9) Hollinella (H.) martensi Crasquin-Soleau 1999; (8) holotype, right lateral view; (9) holotype, right
lateral view.
Photo 15
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5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20
21 22 23 24
25 2627 28
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sp., Geinitzina spp., Pachyphloia robusta Miklukho-Maclay 1954, P. cukurkoyi Sellier de Civrieux andDessauvagie 1965, Lingulonodosaria (?) sp., Frondinodosaria n. sp. aff. plena Sosnina 1976, Rectoglandulina(?) sp., Langella n. sp. aff. venosa Lange 1925, L. cf. ocarina Sillier de Civrieux and Dessauvagie 1965, L. sp.
The fusulinids are completely absent, probably due to a warm temperate climate, and not to evolutionarycontrol, such as the post-keriotheca phase (Sheng, 1992). These smaller forminifera are accompaniedby algae Permocalculus cf. tenellus (Pia, 1937) and pseudo-algae Stacheoides sp.
Bivalves: Dickins (1999) described 10 species from the genera Nuculopsis, Phestia, Edmondia, Dyasmya,?Janeia, ?Liebia, Vnigripecten, Cyrtorostra, Schizodus and ?Astartella from members 2 and 3 of the KhuffFormation.
The following faunal descriptions were added to by Petroleum Development Oman with a number ofunpublished determinations (Aldridge on conodonts; Lethiers on ostracods) and material collectedduring BRGM field work (brachiopod studies by Boullier; cephalopod studies by Glenister). The listnow consists of:
Bryozoans: Fenestella sp., Polypora sp.
Cephalopods, nautiloids: orthoconic nautiloids, Tylonautilus sp., Mooreoceras sp.
Ammonoids: Foordiceras sp., Licroceras sp., Tainoceras sp., Domatoceras? sp., Stacheoceras sp. andPseudohalorites arabicus.
Gastropods: Bellerophon cf. triangularis
Trilobites: Pseudophillipsia lipara, P. stealopyga (Goldring, 1957)
Conodonts: Hindeodus cf. minutus
Ostracods (subsurface): Hollinella aff. herrickana, H. emaciata, H. ulrichi, H. gibbosa
The marine fauna of the exposed lower Khuff Formation notably includes cephalopods, brachiopods,conodonts, ostracods and bivalves, which support a Middle Permian Wordian age (Angiolini et al.,1998, 2001, 2003b; Angiolini and Bucher, 1999; Crasquin-Soleau et al., 1999). The updated smallerforaminifera confirm a Middle Permian age (Wordian and Capitanian, Murgabian and Midian), asindicated by the appearance of Multidiscus (see Reitlinger, 1965; Kotlyar et al., 1989; Vachard et al.,2002), and the specific diversity of the Langella. In addition, conodont fauna from uppermost levels(Khuff member 3) suggests a late Wordian age (Angiolini et al., 2003b).
Photo 15 continued:(10-11) Jordanites lordi Crasquin-Soleau 1999; (10) holotype, right lateral view; (11) right lateral view.(12) Perprimitia brevirostris Schneider 1958; left lateral view.(13) Sargentina minuta Wang 1978; left lateral view.(14-15) Hollinella (H.) herrickana (Girty 1909); (14) right lateral view; (15) left lateral view.(16) Sargentina wautersi Crasquin-Soleau 1999; holotype, left lateral view.(17-18) Sargentina transita (Kozur, 1985); (17) left lateral view; (18) left lateral view(19-20) Cavellina huqfensis Crasquin-Soleau 1999; (19) left lateral view; (20) holotype, left lateral view.(21-22) Cavellina boomeri Crasquin-Soleau 1999; (21) holotype, left lateral view; (22) paratype, left lateral
view.(23) Cavellina gerryi Crasquin-Soleau 1999; holotype, left lateral view.(24) Bairdia omanensis Crasquin-Soleau 1999; holotype, right lateral view.(25) Sulcella arabica Crasquin-Soleau 1999; holotype, left lateral view.(26) Acratina diffusa Schneider 1959; left lateral view.(27-28) Fabalicypris parva Wang 1978; (27) right lateral view; (2) right lateral view.
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PALAEOCLIMATIC EVOLUTION
The Lower to Middle Permian succession of the Haushi-Huqf Uplift records a significant change fromglacial-arid to warm-humid climatic conditions in about 25 million years, inferred from palaeontological,sedimentological and petrographical indicators.
The Al Khlata diamictites were deposited during the earliest Permian climax of the Gondwananglaciation, whereas the topmost interval of the unit is related to glacial retreat and concomitant sea-level rise in the late Sakmarian, with rapid evolution from glacial to temperate climates around theTastubian-Sterlitamakian boundary (Angiolini et al., 2003a, b). The overlying Sakmarian Saiwanbrachiopod fauna is dominated by large and thick-shelled spiriferids with Gondwanan affinity, andhas a generally low to moderate diversity, with a Permian Ratio of 0.57 (Angiolini et al., 1997). Ecosystemdevelopment in the Saiwan Formation records a rapid increase in temperature at the end of theGondwanan deglaciation, with a shift towards temperate conditions in the late Sakmarian (Angioliniet al., 2003a). Such a climatic evolution was also observed in subsurface palynofloras by Stephensonand Osterloff (2002).
The palaeoflora contained in the Upper Gharif Formation suggests much warmer and humid settingsat the beginning of the Middle Permian (Broutin et al., 1995), with permanent precipitation and shortdry season (Fluteau et al., 2001). Furthermore, Middle Permian sandstones of the Haushi-Huqf Upliftdocument a marked increase in mineralogic stability which is chiefly ascribed to more intense chemicalweathering with time, fostered by progressively warmer and humid climates after the end of theGondwanan glaciation and onset of spreading in the Neo-Tethys Ocean.
Such a climatic trend towards higher temperatures continued during deposition of the Khuff Formation,unconformably capped by Triassic laterite/bauxite palaeosols. The Middle Permian Khuff brachiopods(predominantly thin-shelled productids) are significantly diversified (Permian Ratio of 1.57), with amixture of wide-ranging, Paleoequatorial, Cimmerian, and Gondwanan genera indicating a consistent
Photo 16 (facing page): Wordian algae and smaller foraminifera of the Khuff Formation (Photos byDaniel Vachard).(1) Permocalculus cf. tenellus (Pia, 1937). Oblique section. Sample 13A, Photo 3.32, magnification x32.(2) Langella n. sp. aff. venosa Lange, 1925. Axial section. Sample 13A, photo 3.25, magnification x55.(3) Langella cf. ocarina Sillier de Civrieux and Dessauvagie 1965. Subaxial section,. Sample 13, photo
3.20, magnification x78.(4) Frondinodosaria n sp. aff plena Sosnina, 1976. Subaxial section. Sample 13A, photo 3.27, magnification
x78.(5) Langella cf. Oblique section. Sample 13A, photo 3.29, magnification x60.(6) Rectoglandulina (?) sp. Oblique section passing by an aperture. Sample JR 95.6, photo 3.24,
magnification x60.(7) Rectoglandulina (?) sp. Oblique section. Sample JR 95.6, photo 3.21, magnification x60.(8) Pachyphloia robusta Miklukho-Maclay, 1954. Subsagittal section. Sample 13, photo 3.19, magnification
x75.(9) Pachyphloia robusta Miklukho-Maclay, 1954. Subfrontal section. Sample 13, photo 3.19, magnification
x75.(10) Pachyphloia robusta Miklukho-Maclay, 1954. Oblique section. Sample 13, photo 3.10, magnification
x75.(11) Pachyphloia cukurkoyi Sellier de Civrieux and Dessauvagie, 1965. Subsagittal section. Sample 13A,
photo 3.26, magnification x73.(12) Multidiscus cf. arpaensis Pronina, 1988. Axial sparitized section (bottom left) with an ostracod
valve (top right) and Permocalculus sp. (center). Sample JR 95-6, photo 3.22, magnification x75.(13) Fertile Permocalculus cf. tennellus (left) and Langella sp. (right) with several fragments of mollusks
(bottom and top left). Sample 13A, photo 3.31, magnification x47.
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increase of water temperatures (Angiolini et al., 2003b). Of great significance is the invasion of a largenumber of Palaeoequatorial genera (about 35%), which are good indicators of warm-water temperatures(Archbold and Shi, 1995). Khuff bivalves comprise cosmopolitan genera and suggest mild and equablewater temperatures (Dickins, 1999). Finally, Khuff ostracodes belong to the thermosphere, and are typicalof the intertropical zone.
All these climatic indicators suggest warm temperatures, in apparent contrast with the low diversity offoraminiferal and coral assemblages. The absence of fusulinids may be explained by the occurrence ofanomalously high water temperature and nutrient increase. This may also cause a drastic drop in coralbiodiversity. High quartz content at the base of the Khuff Formation indicates that alteration andpedogenesis were progressively more active with time on a wide Arabian area, including all possiblesources of Khuff detritus (Angiolini et al., 2003b).
Climatic changes inferred from palaeontologic and petrographic indicators in Interior Oman has beenascribed to the northward latitudinal shift of Northern Gondwana coupled with the global warmingdocumented from Early to Late Permian (Angiolini et al., 2003b).
CONCLUSIONS
The Al Khlata, Saiwan, redefined Gharif and lower Khuff formations in the Haushi-Huqf outcrops ofOman present the most complete exposure of the Lower and Middle Permian succession in the ArabianPeninsula. They show the passage from the glacial environments of the Al Khlata Formation to theMiddle Permian Khuff carbonate platform. In this study two marine formations are biostratigraphicallydated with some degree of confidence. The older Saiwan Formation (= Lower Gharif Member) is EarlyPermian late Sakmarian in age, and contains MFS P10 (late Sakmarian, Sharland et al., 2001). Thisflooding event is recalibrated at about 284 Ma based on the Sakmarian stage boundaries (betweenabout 287 to 280.3 + 2.6 Ma; Jin et al., 1997). The second marine formation corresponds to the basalcarbonates of the Khuff Formation that are Middle Permian Wordian in age (about 270-260 Ma; Jin etal., 1997). Between the two dated marine formations, the age of the continental redefined GharifFormation is not well constrained, but would range from Early Permian (Artkinsian) to Middle Permian(Roadian/early Wordian).
The Upper Carboniferous-Lower Permian Al Khlata Formation produces oil in Oman, and correspondsto the hydrocarbon-bearing Unayzah C and B members in Saudi Arabia (Stephenson et al., 2003). ThePermian Saiwan and redefined Gharif formations pass laterally (in part) to the subsurface GharifFormation of Interior Oman, and the Unayzah A Member of Saudi Arabia (Stephenson et al., 2003).These subsurface rock units also constitute important hydrocarbon sandstone reservoirs. The presentedage estimates, together with the lithofacies and interpreted depositional environments, provideconstraints for the subsurface sequence stratigraphic architecture and chronostratigraphic correlationsin the Arabian Peninsula.
ACKNOWLEDGEMENTS
The authors wish to thank Professors Marco Balini, Eduardo Garzanti, Alda Nicora and Andrea Tintorifor sharing their results and interpretations in this study. The authors also thank Peter Osterloff andMike Stephenson for their useful comments on the manuscript.
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