Permian to Cretaceous radiolarian biostratigraphic data from theHawasina Complex, Oman Mountains

P. DE WEVER1 Ch. BOURDILLON-de GRISSAC2 & F. BECHENNEc3

1 CNRS UR 1315, Universite P. M. Curie, T 15-16 E4, F-75252 ParisCedex 05, France

2 BRGM-SGN-GEO, F-45 060 Orleans, France3 BRGM, 10 Rue Picheri, 44300 Nantes, France

Abstract: The analysis of foraminifera and radiolaria in 3000 carbonate and 150 siliceousrock samples from the Oman Mountains results in revision of the existing stratigraphy andsupports the definition of new units. In the Hawasina allochthonous unit the main resultsare as follows: (i) Permian bedded chert exists near the base of the sequence and is thusthe first Permian bedded chert occurrence reported from the Tethyan region); (ii) animportant volcanic event is dated as Triassic; (iii) bedded chert horizons are dated asLiassic; (iv) the thick turbiditic sequence has been divided into several units of Middle andLate Jurassic age. In the Samail ophiolite: (i) the ages of four tectonic episodes wereestablished from the beginning of oceanic spreading (Albian-Early Cenomanian), to theobduction of the ophiolitic nappe (Campanian).

Around 3000 limestone and chert samples werecollected for palaeontological analysis duringthe BRGM mapping project (1/100000) in theCentral Oman Mountains. Carbonate rocksyielded foraminifera, ostracods, algae; alsomacrofauna; while the siliceous rocks yieldedidentifiable radiolarians.

Radiolarians were extracted from rocksamples with established techniques (De Weveret al. 1979b; 1982b) that use extremely dilutehydrofluoric acid (1 to 0.1%), and successiveetching. The ages of samples were establishedusing different sets of data handled by micro­computers. (Vrielynck & Granlund 1988,Vrielynck 1989) and from published biozona­tions or unpublished data (Pessagno 1977; DeWever et al. 1979a; Baumgartner et al. 1980; DeWever, 1981a,b,c, 1982 a,b; Blome, 1983;Baumgartner 1984, 1987; De Wever & Micon­net, 1985; De Wever et al. 1985; De Wever &Cordey, 1986; De Wever et al. 1986; Aita, 1987;De Wever et al. 1987a,b, 1988a,b; Pessagno etal. 1984, 1987). For each species we used therange of its acrozone, and for each sample weused the concurrent range zone.

Geological setting

The Oman Mountains comprise an arcuate chain(700 km long x 50-140 km wide), from theMusandam Peninsula in northwest to the Surregion in the southeast (Fig. 1). The mountainsculminate in the 3000 m high Jabal Akhdar and

are flanked to the north by the Gulf of Oman orby the Batinah plain, and to the south by thedeserts of interior Oman. The mountains wereuplifted mainly during Mio-Pliocene.

The following main units are recognized fromthe bottom to the top: Upper Proterozoic crys­talline basement in the southeast (Jabal Ja'alanand Qahlat region); the 'A autochtonous unit',transgressive on the basement, this comprisesvolcanic and sedimentary rocks, deformedduring late Panafrican and Hercynian orogenicevents; and the 'B autochtonous unit', mainlycomposed of transgressive carbonates dated asPermian to Cretaceous. The carbonates weredeposited on the northeast edge of the Arabianplatform and were deformed and locally meta­morphosed during the Eo-alpine orogenesis;the Hawasina nappes are composed of mainlydeep-water sedimentary and volcanic rocks ofPermian to Cretaceous age. They represent afragment of the passive margin of the SouthernTethys that was overthrust onto the Arabianplatform during Late Cretaceous time. TheSamail ophiolite formed during Albian, Ceno­manian to Senonian times (De Wever et al.1988b), and was also obducted onto the Arabianplatform during Campanian- Early Maastrichtiantime (Beurrier et al. 1987). The 'Neo-Autoch­thonous unit' is transgressive on all the previousunits. Sedimentation began during Middle toLate Maastrichtian and continued until Miocenetime (Burdigalian). The eastern and centraloutcrops of these units, were studied by the

From ROBERTSON, A. H. F., SEARLE, M. P. & RIES, A. C. (eds), 1990,The Geology and Tectonics of the Oman Region.Geological Society Special Publication No 49, pp 225-238

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RADIOLARIAN BIOSTRATIGRAPHIC DATA 227

Bureau de Recherches Geologiques et Minieres(Bechennec 1987; Bechennec et al. 1990).

The Hawasina nappes are sandwichedbetween the overlying Samail ophiolite nappeand the underlying 'autochthonous' sequencesof the Arabian platform (Jebel Akhdar andSaih Hatat) (Fig. 1). The sedimentary rocks ofthe Hawasina nappes document the Mesozoicevolution of the northeastern Arabian continen­tal margin and the adjacent Tethys ocean.During Mezosoic time the Hawasina basin wasflanked to the northeast (oceanwards) by car­bonate platform build-ups, termed the OmanExotics (Glennie et al. 1974; Graham 1980a,b;

Searle & Graham 1982; Kasmin et al. 1986;Watts & Garisson 1986; Bernoulli & Weissert1987). Associated with these units are Permianand Mesozoic shelf-edge and condensed sea­mount facies (e.g. Hallstatt Limestones; Calon& Tozer in Bernoulli & Weissert 1987. Thelower Hawasina nappes include Triassic, Jurassicand Cretaceous base-of-slope ba~hyal sediments(e.g. Hamrat Dum, Wahrah),'and are locallyoverlain by massive sandstone successions. In­tact Mesozoic sequences including Cretaceouspelagic sediments are also found in the highestHawasina units (AI Aridh and Oman Exotics).Here we will use the stratigraphy proposed by

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Fig. 2. Composite (estimated) lithostratigraphic column of the Hamrat Duru Group with position ofproductive radiolarian samples (numbers) (and "R" on columns), and other palaeontological groups(Foraminifera: "F", Pelecypods: "P", Calpionellids: "Calp", Ammonites: "A")

228 P. DE WEVER ET AL.

Bechennec (1987), as depicted on the Geo­logical maps of Oman (Bechennec et al. 1986;Villey etal. 1986), comprising the Hamrat Duru,Al Aridh and Umar Groups:

Hamrat Duru Group

Two main types of facies exist in the HamratDuru Group; siliceous (i.e. Wahrah Formation)and calcareous (i.e. Guwayza Formation) (Fig.2).Siliceous facies of the Hamrat Duru Group (in­cluding the Wahrah Formation). The WahrahFormation mainly comprises siliceous sediments(originally siliceous or diagenetically silicified).Most of the siliceous horizons have been datedby radiolarians. Also, Callovian-Oxfordianforaminifera were found in silicified calcareousturbidites overlying the lowest silicified se­quence (Bechennec 1987; Bechennec et al.1990). Chert levels overlying this thick turbiditicsequence yielded the following radiolarians ofmainly Late Jurassic (Maim) age.

DJ 359E: MaIm to Neocomian with :Alievium helenae SCHAAF, Archaeospong­oprunum sp., Pantanellium sp. cf. P. ultra­sincerum PESSAGNO. Pantanellium lanceola(PARONA) gr., Archaeodictyomitra apiaria(RUST), Hsuum sp., Podobursa (form withnumerous and long equatorial spines), Saitoumelegans DE WEVER

FB 288B: Middle Callovian to MiddleOxfordian including: Pantanellium lanceola,(PARONA) gr., Tritrabs casmaliaensis

PESSAGNO, Archaeodictyomitra sp. ,Hsuum brevicostatum (OZVOLDOVA),Hsuum maxwelli PESSAGNO gr., Mirifusussp. cf. M. fragilis BAUMGARTNER,Mirifusus guadalupe'nsis PESSAGNO, Sai­toum sp., Spongocapsula sp.

MV 493: ?Callovian to Tithonian with :Acanthocircus dicranacanthos SQUINABOL,Alievium helenae SCHAAF, Angulobracchia(?) portmani BAUMGARTNER, Emiluviachica FOREMAN, Pantanellium lanceola(PARONA) gr. (ancestral form), Pantanelliumsp. (with circular polar spines), Triactomacornuta BAUMGARTNER, Triactomatithonianum RUST, Zartus ? sp., Archaeo­dictyomitra apiaria (RUST), Bernoulliusdicera (BAUMGARTNER), Hsuum sp. (H.obispoensis gr.), Mirifusus mediodilatatus(RUST), Ristola altissima (RUST), Parvicin­gula boesii (PARONA), Parvicingula cosmo­conica (FOREMAN), Podobursa triacanthaFISCHLI, Pseudodictyomitra carpatica (LO­ZYNYAK), Syringocapsa limatum (FORE­MAN), Thanarla pulchra (SQUINABOL);Silicified turbidites overlying this horizon

yielded Callovian-Oxfordian foraminifera(Bechennec 1987) (Fig. 3)

Thick sequence of chert of the middle part ofthe Wahrah Formation yielded numerous radio­larians of Tithonian to Hauterivian age.

FB 293: Bathonian to middle Tithonian (poss­ibly Kimmeridgian), with : Acanthocircussuboblongus (YAO), Eucyrtis micropora gr.(SQUINABOL), Hsuum brevicostatum

Fig. 3. Radiolarians from Permian to Liassic samples.1. Follicuculus scholasticus ORMISTON & BABCOCK (morphotype 2, sensu Ishiga et al. 1986), x100 (FB

703, fig. 2), Permian, Al Jil Formation, Hamrat Duru Group.2. Follicuculus scholasticus ORMISTON & BABCOCK (morphotype 1, sensu Ishiga et al. 1986), x165 (FB

703, fig. 2), Permian, Al Jil Formation, Hamrat Duru Group.3. Follicuculus monacanthus ISHIGA & IMOTO, x100, (FB 703, fig. 2), Permian AI Jil Formation, Hamrat

Duru Group.4. Falcispongus aft. rostratus DUMITRICA, x125 (JLM 136C, fig. 3), Triassic (Ladinian), Aquil Formation,

Umar Group.5. "Capnuchosphaera? sp. B" in DE WEVER et al. 1979, x125 (JLM 136C, fig. 3), Triassic (Ladinian), Aquil

Formation, Umar Group.6. Sarla aff. vetusta PESSAGNO, x100, (DJ 214F, fig. 4), Triassic, Sayfam Formation, AI Aridh Group.7. Plafkerium cochleatum (NAKASEKO & NISHIMURA), x80, (JLM 136C, fig. 3), Triassic (Ladinian),

Aquil Formation, Umar Group.8. Spongostylosphaera hellenica (DE WEVER), x120, (JLM 136C, fig. 3), Triassic (Ladinian), Aquil

Formation, Umar Group.9. Latium sp. x190, (JLM 136C, fig. 3), Triassic (Ladinian), Aquil Formation, Umar Group.

10. Jacus anatiformis DE WEVER, x200, (DJ 213D, fig. 4), Liassic Buwajdah Formation, Al Aridh Group.11. Napora sp. x190, (FB 577B, fig. 2), Liassic, Guwayza Formation, Hamrat Duru Group.12. TrWus elkhornensis PESSAGNO & BLOME, x230, (DJ 213D, fig. 4), Liassic, Buwajdah Formation, AI

Aridh Group.

RADIOLARIAN BIOSTRATIGRAPHIC DATA 229

230 P. DE WEVER ET AL.

OZVOLDOVA, Parvicingula boesii (PAR­ONA) gr., Podobursa triacantha (FISCHLI)gr., Saitoum corniculum DOE WEVER;DJ 58C: Kimmeridgian? to Neocomian, with:Acanthocircus dicranacanthos (SQUINABOL),Alievium helenae SCHAAF, Emiluvia chicaFOREMAN, Pantanellium lanceola (PARO­NA) gr. (morphotype with thin spines),Archaeodictyomitra excellens (TAN), Par­vicingula boesii (PARONA) gr., Parvicingulacosmoconica (FOREMAN), Podobursahelvetica (RUST), Podobursa chandrikaKOCHER, Protunuma costata (ZITIEL),Ristola procera (PESSAGNO), Saitoum cor­niculum DE WEVER, Thanarla conica(ALIEV)

MB 343: Oxfordian to Tithonian with :Archaeospongoprunum sp., Tetraditryma cor­ralitoensis (PESSAGNO), Triactoma blakei(PESSAGNO), Triactoma jonesi (PES­SAGNO), ? Amphipyndax sp., Archaeodic­tyomitra apiaria (RUST), Eucyrtis micropora(SQUINABOL) gr., Hsuum sp., Mirifusussp., Podobursa spinosa (OZVOLDOVA)

MB 371: Middle to Late Tithonian with :Acanthocircus dicranacanthos (SQUIN­ABOL), Archaeospongoprunum tehamaensisPESSAGNO, Emiluvia chica FOREMAN,Emiluvia orea BAUMGARTNER, Pantanel­lium lanceola (PARONA), Archaeodictyo­mitra apiaria (RUST), Parvicingula boesii(PARONA), Pseudodictyomitra carpatica(LOZYNYAK), Saitoum elegans DEWEVER, Sethocapsa trachyostracaFOREMAN.

XG 440: Tithonian with : Acanthocircusdicranacanthos (SQUINABOL), Alieviumsp. cf. A. helenae SCHAAF, Emiluviapessagnoi FOREMAN, Pantanellium lan­ceola (PARONA) gr., Archaeodictyomitraapiaria (RUST), Ristola altissima (RUST)

XG 455: Tithonian to Valanginian withAcanthocircus dicranacanthos (SQUI­NABOL), Mirifusus sp. cf. M. mediodilatatus(RUST)

MB 374: Tithonian to Berriasian with: Acan­thocircus dicranacanthos (SQUINABOL),Alievium helenae SCHAAF, Archaeospong­oprunum sp., Emiluvia oreaBAUMGARTNER, Pantanellium lanceola(PARONA) gr. (ancestral morphotype),Triactoma jonesi (PESSAGNO), ? Parvicin­gula cosmoconica (FOREMAN), Podobursatriacantha (FISCHLI) gr.

MB 378: Berriasian to Middle Hauterivianwith Acanthocircus dicranacanthos(SQUINABOL), Pantanellium lanceola(PARONA) gr., Parvicingula cosmoconica(FOREMAN)

MB 395: Late Tithonian to Barremian with:Archaeodictyomitra apiaria (RUST), A. vul­garis PESSAGNO, A. excellens (TAN),Emiluvia chica FOREMAN, Alieviumhelenae SCHAAF, Acanthocircus dicranacan­thos (SQUINABOL), Pantanellium lanceola(PARONA) gr., Parvicingula boesii (PAR­ONA), Thanarla conica (ALIEV), Angulo­bracchia (?) portmanni BAUMGARTNER.

MB 475: Tithonian to Middle Valanginianwith: Acanthocircus dicranacanthos (SQUI­NABOL), Pantanellium lanceola (PARONA)gr., Archaeodictyomitra apiaria (RUST),Mirifusus mediodilatatus (RUST), Ristola altis­sima (RUST), Ristola sp. cf. R. cretacea(BAUMGARTNER).

MB 476: Tithonian to Hauterivian with :Acanthocircus dicranacanthos (SQUI­NABOL), Pantanellium lanceola (PARONA)gr. (ancestral form), Syringocapsa limatumFOREMAN

MB 377: Tithonian to Hauterivian with :Acanthocircus dicranacanthos (SQUI­NABOL), Acanthocircus trizonalis (RUST),Acanthocircus carinatus FOREMAN, Meso­saturnalis multidentatus (SQUINABOL),Pantanellium lanceola (PARONA) gr., Triac­toma hybum FOREMAN, Eucyrtis micropora(SQUINABOL) gr., Pseudodictyomitra sp.

JLM 526: Tithonian to Hauterivian with :Acanthocircus dicranacanthos (SQUI­NABOL), Acanthocircus carinatus FORE­MAN, Pantanellium lanceola (PARONA)gr., Archaeodictyomitra apiaria (RUST) ,Mirifusus sp. cf. M: mediodilatatus (RUST),Parvicingula boesii (PARONA) gr.

JLM 527: Kimmeridgian to Tithonian with:Emiluvia chica FOREMAN, Emiluviapessagnoi FOREMAN, Tetratrabs bulbosaBAUMGARTNER, Eucyrtis micropora gr.(SQUINABOL), Obesacapsula rotunda(HINDE), Mirifusus mediodilatatus (RUST)s.l., Parvicingula dhimenaensis BAUMG­ARTNER, Parvicingula boesii (PARONA),Podocapsa amphitreptera FOREMAN Podo­bursa triacantha (FISCHLI), Ristola altissima(RUST) (without nodular overgrowth), Spon­gocapsula palmerae PESSAGNO.

RADIOLARIAN BIOSTRATIGRAPHIC DATA 231

MV 831: Late Jurassic to Neocomian with:Pantanellium lanceola (PARONA) gr., (ovalcentral shell with thin polar spines),Archaeospongoprunum sp., Ristola altissima(RUST), Napora sp. cL N. praespinifera(PESSAGNO)

MV 490: Berriasian to lower Valanginianwith: Acanthocircus dicranacanthos (SQUI­NABOL), Alievium helenae SCHAAF, Ar­chaeodictyomitra apiaria (RUST), Naporabukryi PESSAGNO;MV 1113: Neocomian with: Archaeodic­tyomitra lacrimula (FOREMAN), Eucyrtissp. cf. E. ptyctum RIEDEL & SANFILIPPO,Ristola altissima (RUST), Parvicingula gr.(massive form)

MB 353A: Tithonian to Neocomian with:Acanthocircus sp. (with two separate spines),Archaeospongoprunum tehamaensis PES­SAGNO, Emiluvia chica FOREMAN,Pantanellium lanceola (PARONA), Arc­haeodictyomitra sp. cf. A. lacrimula (FORE­MAN), Archaeodictyomitra apiaria(RUST), Katroma ? sp., Parvicingula boesii(PARONA), Pseudodictyomitra carpatica(LOZYNYAK), Sethocapsa trachyostracaFOREMAN.Partly silicified calcareous turbidites overlying

the chert sequence yielded reworked LowerNeocomian Early Cretaceous foraminifera ofshallow water affinities (Bechennec 1987). Theoverlying sequence, composed of unsilicifiedturbidites was dated as late Neocomian by for­aminifera (Bechennec 1987).

The upper chert sequence of the WahrahFormation yielded radiolarians of lateNeocomian (Early Cretaceous) to early Aptian(Late Cretaceous) age.

MB 125 A: Late Hauterivian to Early Aptianwith: Pantanellium lanceola (PARONA) gr.,Eucyrtis tenuis (RUST), Eucyrtis micropora(SQUINABOL) gr., Archaeodictyomitralacrimula (FOREMAN)

XG 457: Barremian to Early Aptian with:Archaeodictyomitra lacrimula (FOREMAN),Eucyrtis micropora (SQUINABOL) gr.,Crolanium pythiae SCHAAF.

Calcareous facies of the Hamrat Duru

Group (including Guwayza Formation)The base of the sedimentary part of the AI JilFormation (i.e. chert overlying pillow basalt)has been dated (De Wever et al. 1988a) asMurghabian (Mid-Late Permian) by radio-

larians (in sample FB 703): Follicucullusscholasticus ORMISTON & BABCOCK(morphotypes 1 and 2 of Ishiga et al. 1986), F.sp. cL F. ventricosus ORMISTON &BABCOCK, Follicucullus monacanthusISHIGA & IMOTO and Triassocampe-likemorphotype. This association correlates withlate Gadalupian samples in Japan (Ishiga et al.1986; Ishiga 1986) and those in the Urals andTexas (Nazarov & Ormiston 1985).

Some other fossils were also found in associ­ated reworked reefal limestone blocks (DeWever et al. 1988a) of Late Murghabian age (=Late Kazanian within the Middle Guadalupian).These fossils are bryozoans (Fenestellidae),echinoderms (crinoids) ~ gastropods, ostracodescorals, algae (abundant, along with Tubiphytesobscurus MASLOV, Mizzia velebitanaSCHUBERT), benthic foraminifers (Neosch­wagerina margaritae, Globivalvulina vonder­schmidti, Agathammina pusilla, Staffella sp.,Geinitzina sp., Pachyploia sp., Nankinella sp.)The base of the Aj2C (i.e. upper Al Jil For­mation) locally includes limestone horizonswith Triassic foraminifera and pelecypods(Bechennec 1987).

The upper part of the Al Jil (Aj2C) has beendated as Middle to Upper Triassic by radio­larians, as follows (Fig. 6).

DR 29: Baumgartneria sp. aff. B. retrospinaDUMITRICA (with a central spine shorterthan on holotype), Eptingium sp. cf. E.manfredi DUMITRICA, Falcispongus cal­caneum DUMITRICA, Plafkerium sp.;

FB 194: Archaeospongoprunum sp., Eptin­gium sp. cL E. manfredi DUMITRICA, ?Plafkerium sp.

FB 203G: Plafkerium sp., undescribedmorphotypes belonging to the Sarlinae (withtwo spines), Triassocampe ? sp., Conodontfragment

FB 343A: Capnuchosphaera lea DEWEVER, Capnuchosphaera mexicanaPESSAGNO, Capnuchosphaera sp. cf. C.puncta DE WEVER, Capnuchosphaeratheloides DE WEVER, Sarla sp.,Triassocampe sp.,

FB 199: Capnuchosphaera triassica DEWEVER, Xiphotheca ? sp.

FB 566: Pseudostylosphaera sp. cf.P. hellenicum (DE WEVER), Baumgartneriasp. cf. B. curvispina DUMITRICA,Hinedorcus sp. cf. H. alatus DUMITRICA,

232 P. DE WEVER ET AL.

RADIOLARIAN BIOSTRATIGRAPHIC DATA 233

KOZUR & MOSTLER, Plafkerium sp.,Plafkerium hindei PESSAGNO, Plafkeriumsp. cf. P. hindei PESSAGNO, Sepsagonlongispinosum DUMITRICA, KOZUR &MOSTLER, Triassocampe sp.

The lower Matbat Formation (Mb1) has beendated. as Triassic by pelagic pelecypods(Halobia) in the biomicritic levels (Bechennec1987). Some of the Permian (UpperMurghabian) microfauna are reworked.

The upper Matbat Formation (Mb1) is datedas Late Triassic (Norian- Rhaetic) by pelagicpelecypods (Halobia), Crinoidea, benthic for­aminifera (from reefal, platform and deep watersettings) (Bechennec 1987). Some Permianmicrofossils were also found in re-workedcalcareous sediments throughout this sequence.

The cherts at the base of the Guwayza For­mation has been dated as Late Liassic to earlyDogger by radiolarians: (FB 557 B) Bernoulliussp. (with straight spines), Tethis sp. aft. T.stolata DE WEVER (with cephalis more clearlydistinct than the holotype and with longitudinalribs), '? Tethis sp. ' in DE WEVER 1982a, Trilluselkornensis PESSAGNO & BLOME, and otherNassellaria g. sp. indet.

The siliceous base of the Sid'r Formation(base of Si1) has been dated as Kimmeridgianor Tithonian by radiolarians : (FB 748 B)Acaeniotyle diaphorogona FOREMAN,Emiluvia chica FOREMAN, Emiluvia pes­sagnoi FOREMAN, Emiluvia sedecimporataelegans (WISNIOWSKI), Emiluvia sedecim­porata salensis (PESSAGNO), Pantanellium

lanceola (PARONA) gr., Tritrabs worzeli(PESSAGNO), Tetraditryma sp. cf. T. pseudo­plena BAUMGARTNER, Tritrabs casmaliensis(PESSAGNO), Podobursa triacantha (FIS­CHLI) gr., Podocapsa amphitreptera FORE­MAN, Napora sp. Neither Higumastra imbricataOZVOLDOVA, nor any representative ofAndromeda were found, confirming an upper­most Jurassic age.

Some calcareous levels within this siliceouspart yielded Late Tithonian- BerriasianCalpionellids (Bechennec 1987).

The silicified calcareous levels (mid and upperpart) of Si1 (lower Sid'r Formation) yielded nopaleontological data.

The mid Sid'r Formation (Si2) has been datedas Upper Albian to Cenomanian by foraminifera(Bechennec 1987).

The silicified calcareous horizons in the upper­most part of Sid'r Formation (Si2c) were barren.

The Nayid Formation has been dated withplanktonic foraminifera (Bechennec 1987) as:mid Cenomanian to Early Turonian in the lowerpart; Early to middle Turonian in the middlepart; Late Turonian to Early Senonian in theupper part.

The Umar group

In the upper part of the Sini Formation (UrnV2)calcareous olistoliths have been dated as Triassic(Carnian) by neritic microfossils (Bechennec1987) including algae, corals and foraminifera.No radiolaria were found in the Sini Formation(Fig. 5).

Fig. 4. RadioIarians from Liassic to Cretaceous.1. Parahsuum simplum YAO, x190, (DJ 213D, fig. 4), Liassic, Buwaydah Formation, AI Aridh Group.2. Nassellaria gen. et sp. indet. x150, (FB 577B, fig. 2) Liassic, Guwayza Formation, Hamrat Duru Group.3. "Gen. sp. indet. I" in DE WEVER, 1982, x150, (FB 577B, fig. 2), Liassic, Guwayza Formation, Hamrat

Duru Group.4. Drulanta sp. cL mostleri YEH, x150, (DJ 213D, fig. 4), Liassic, Buwaydah Formation, AI Aridh Group.5. Canoptum anulatum PESSAGNO & POISSON, x150, (FB 577B, fig. 2), Liassic, Guwayza Formation,

Hamrat Duru Group.6. Droltus (?) sp. x330, (FB 577B, fig. 2), Liassic, Guwayza Formation, Hamrat Duru Group.7. Ristola altissima (RUST), x95, (MV 493, fig. 2), Late Jurassic to Early Cretaceous, Wahrah Formation,

Hamrat Duru Group.8. Thanarla conica (ALIEV), x240, (MY 841, fig. 4), Neocomian, Buwaydah Formation, Al Aridh Group.9. Parahsuum simplum YAO, x190, (DJ 213D, fig. 4), Liassic, Buwaydah Formation, AI Aridh Group.

10. Pseudodictyomitra carpatica (LOZYNYAK), x180, (MV 493, fig. 2), Late Jurassic to early Cretaceous,Wahrah Formation, Harnrat Duru Group.

11. Pseudoaulophacus putahensis PESSAGNO (?), x145, (DR 40, fig. 4), Senonian, Mussalah Formation, AIAridh Group.

12. gen. sp. indet., (DJ 213D, fig. 4), Liassic, Buwaydah Formation, AI Aridh Group.13. Alievium helenae SCHAAF, x250, (MY 490, fig. 2), Berriasian-Valanginian, Wahrah Formation, Hamrat

Duru Group.14. Pantanellium lanceola (PARONA), x150, (MY 493, fig. 2), Late Jurassic to Early Cretaceous, Wahrah

Formation, Hamrat Duru Group.15. Alievium praegallowayi PESSAGNO, x190, (DR 40, fig. 4), Senonian, Mussalah Formation, AI Aridh

Group.

234 P. DE WEVER ET AL.

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~--------t;~~~-FB69-213 MB316dLM 1049 R Up. TRIASSIC

Dr 316c RMJ935 RwFJLMI050MVBI8 RwF RwTRIASSICJL Mc136c

Fig. 5. Composite (estimated) lithostratigraphic column of the Umar Group with position of productiveradiolarian samples (numbers) ("R" on columns), and of reworked Foraminifera "RwF"

The base of the Aqil Formation has beendated as Triassic, based on the following.

DR 316: Carnian (or Norian) with:Capnuchosphaera deweveri NAKASEKO &NISHIMURA, Capnuchosphaera lea DEWEVER

JLM 136C: Ladinian with: Eptingium man­fredi DUMITRICA, Falcispongus sp. aft.F. falciformis DUMITRICA (spines morecircular than holotype), Pentaspongodiscussp. cf. P. rarauana DUMITRICA, Triasso­campe sp. cf. T. deweveri DUMITRICA,Capnuchosphaera sp. (with a somewhat tri­angular central shell), Pseudostylosphaerahellenica (DE WEVER).

JLM 1050: Ladinian : Baumgartneria sp. aft.B. retrospina DUMITRICA (with somewhatshorter spines than the holotype),Baumgartneria retrospina DUMITRICA,Oertlispongus sp. aft. O. inaequispinosusDUMITRICA (with strongly twisted spines),Triassocampe sp., Pseudostylosphaera sp.

MV 818: Middle to Late Triassic: Triasso­campe sp., Plafkerium sp. cf. P. confluensDUMITRICA, KOZUR & MOSTLER,Plafkerium sp(p), Sarla sp., Spongoserrula

rarauana DUMITRICA, Eptingium manfrediDUMITRICA.MV 935: Middle to Late Triassic with:Oertlisponginae

FB 69: Triassic? with: Palaeosaturnalis sp.(or Pseudoheliodiscus sp.?), Heliosaturnalissp.,JLM 1049: Triassic with: Pentaspongodiscussp. cf. P. dercourti DE WEVER (with numer­ous small bifides spines on central shell),Capnuchosphaera sp. (two of the coplanararms are orthogonal, as in sample JLM 136 C)

MB 316C: Carnian to Norian with: Pseudo­heliodiscus sp., Triassocampe sp.,Capnuchosphaera triassica DE WEVER,Heliosaturnalis sp. and one radiolarian frag­ment with a spindle-shaped spine withtuberculate ribs.

The base has been dated as Late Triassic bythe following.

FB 679A: Norian with: Capnuchosphaeratricornis DE WEVER, Capnodoce anapetesDE WEVER, Capnodoce sp. aft. C. anapetesDE WEVER (morphotype illustrated byBlome in Middle to Late Norian strata inNorth America), Capnuchosphaera deweveri

RADIOLARIAN BIOSTRATIGRAPHIC DATA 235

1::-_-"..,_-",",_-,""",_-"",,_-,"",,_-,...,_c.-:s'__ Dr 40 0

------_.",,-:,..;-:;,,:-;-;:-;,;;--c;::-,,;:-~- Dj 103

:·?f;4LL':'W_-_-_-=-=-_-=-:-1-- Dj 48A

o J

R SENONIAN

ALBIAN

RwF (Rw PERMIAN)

R

RR NEOCOMIAN

RR

£~ ~

~ Ar, :=::=i:;::~:

>­cl(fJ

RRR RwFRR

RR

R

R

NEOCOMIAN

(Rw TRIASSIC)

TITHONIAN

L1A 5

TRIASSIC

P TRIASSIC

Fig. 6. Composite (estimated) lithostratigraphic column of the Al Aridh Group with position of productiveradiolarian samples (numbers) (and "R" on columns), and other palaeontological groups (Foraminifera "F",Pelecypods "P", and reworked Foraminifera: "RwF")

PESSAGNO, Perispongidium (?) tethyus DEWEVER, Syringocapsa sp. cf. S. batodes DEWEVER

XG 469: Late Triassic with: Capnuchosphaeratricornis DE WEVER, Capnuchosphaeraconcava DE WEVER, Capnuchosphaera sp.cf. C. triassica DE WEVER, Xiphothecakarpenissionensis DE WEVER

The middle part of the Aqil Formation hasbeen dated as Liassic by radiolarians.

DR 186: Trillus elkhornensis PESSAGNO &BLOME, Jacus sp. cf. J. anatiformis DEWEVER, Poulpus sp. cf. P. keki DEWEVER and Thetis undulatus DE WEVER.In this part, Late Triassic reefal microfossils(corals, algae, foraminifera) were found inlimestone olistoliths.

The uppermost part of the Aqil Formationhas been dated Neocomian (Hauterivian- EarlyAptian) by radiolarians: (DR 43 B).

Archaeodictyomitra lacrimula (FOREMAN),Praeconocaryomma sp., Pantanellium lan­ceola (PARONA) gr. and Xitus (Novixitus?)sp.

Al Aridh group

Calcareous horizons in the lower part of theSayfam Formation have been dated as Triassicby pelagic Pelecypods (i.e. Halobia) and For­aminifera (Fig. 6) (Bechennec 1987).

The upper part of Sayfam Formation hasbeen dated as Late Triassic (Carnian? to Norian)by radiolarians : (MV 944) : Parasepsagon sp.cf. P. robustus KOZUR & MOSTLER,Triassocampe sp., Capnuchosphaera sp. cf. C.triassica DE WEVER, Hsuum sp. and Sarla sp.cf. S. vetusta PESSAGNO.

The lower part of the Buwaydah Formation(Ar2) has been dated as Late Liassic by radio­larians among which several species are new(work in progress): (DJ 213D, DJ 213J):Parashuum simplum YAO, Pantanellidae spp.

236 P. DE WEVER ET AL.

and (DJ 433E) : Higumastra sp. (fragment), ?Pachyoncus sp., Emiluvia-like, spummellarianswith 6 orthogonal spines, and a multilayeredshell, Pantanellinae sp. (forms with elongatedshell) ; (DJ 213 Q) Pachyoncus sp., Angulobrac­chia sp., Triactoma sp. (morphotype with ameshwork on the proximal part of spines), Kat­roma sp., nassellarians with a square distalmeshwork)

The upper part of the Buwaydah Formationhas been dated as Tithonian to Neocomian byradiolarians.

FB 768: Berriasian to Early Aptian with:Pantanellium lanceola (PARONA) gr.,Archaeodictyomitra apiaria (RUST), Pseudo­dictyomitra carpatica (LOZYNYAK),Thanarla conica (ALIEV)

FB 292E: Tithonian to Hauterivian with:Pantanellium lanceola (PARONA), Ar­chaeodictyomitra sp., Thanarla sp. cf. T. con­ica (ALIEV), Acanthocircus dicranacanthos(SQUINABOL)

FB 137B: Tithonian to Valanginian with:Acanthocircus dicranacanthos (SQUI­NABOL), Pantanellium lanceola (PARONA)gr., Podobursa polylophia FOREMAN,Mirifusus sp. cf. M. mediodilatatus (RUST),Archaeodictyomitra apiaria (RUST)

DR 21H: MaIm to Neocomian with:Pantanellium lanceola (PARONA) gr.,Acaeniotyle sp., Acanthocircus sp., Crucellasp.

FB 769: Tithonian with: Acanthocircusdicranacanthos (SQUINABOL), Pantanel­hum lanceola (PARONA) gr., Podobursa tria­cantha (FISCHLI), Parvicingula cosmoconica(FOREMAN)

The uppermost part of the Buwaydah Forma-tion is dated as Neocomian by radiolarians.

DJ 11: Berriasian to Cenomanian with:Archaeodictyomitra lacrimula (FOREMAN).Archaeodictyomitra apiaria (RUST), Thanarlaconica (ALIEV), Thanarla praeveneta PES­SAGNO, Eucyrtis micropora gr. (SQUI­NABOL)

GH 323: Neocomian with: Ditrabs sp. cL D.sansalvadorensis (PESSAGNO), Eucyrtismicropora gr. (SQUINABOL)

MV 841: Neocomian with: Acaeniotyleumbilicata FOREMAN, Thanarla conica(ALIEV), Spongocapsula palmeraePESSAGNO, Archaespongoprunum sp.; this

fauna is well preserved but specimens arebroken; several species are undescribed.

The Al Ghafat Formation (Ar3) is verycoarse-grained near its base and includes lime­stone olistoliths, which are dated as Late Triassic(Norian to Rhaetian by neritic foraminifera(Bechennec 1987).

In the Mussalah Formation, the chert overly­ing the limestones of the lower part (Ar41)yielded a radiolarian fauna ranging fromTithonian to Neocomian:

DR 152D: Late Tithonian to Hauterivianwith: Acanthocircus dicranacanthos(SQUINABOL)

JM 811: Oxfordian to Valanginian with:Mirifusus sp., Ristola altissima (RUST),Parvicingula boesii (PARONA) gr.The middle part of the Mussallah Formation

is dated as Late Neocomian (Hauterivian toBarremian) by radiolarians : (DR 133 B) :Pantanellium lanceola (PARONA) gr., Cecropsseptemporatus (PARONA), Alievium helenae

SCHAAF, Thanarla elegantissima (CITA)Permian (Murghabian to Djulfian) horizon

limestone olistoliths with foraminifera occur ina coarse detrital olistoliths (Bechennec 1987).

The upper part of the Mussallah Formation isdated as Albian by radiolarians (DJ 103) with:Thanarla conica (ALIEV), Spongocapsula sp.cf. S. perampla (RUST), Emiluvia sp. cf. E.chica FOREMAN, Eucyrtis micropora gr.(SQUINABOL), Napora sp., Mita sp. cf. M.magnifica PESSAGNO, Acaeniotyle dia­phorogona FOREMAN (with a clear inner shellas previously established by OZVOLDOVAand Sykora M. (1984)

The uppermost part of the Mussallah Forma­tion is dated as Senonian (Coniacian?) by radio­larians (DR 40 D): Pseudoaulophacus superbus(SQUINABOL) gr., Pseudoaulophacus flore­sensis PESSAGNO, Eucyrtis micropora gr.(SQUINABOL), Crucella irwini PESSAGNO

Conclusions

The systematic collection of each bedded chertlevel associated with turbidites in the Hawasinaallochthonous unit has led to greatly improvedage dating and recognition of various sedimen­tary and tectonic events.

The main results are as follows:(i) Permian bedded chert exist near the base

of the Hawasina Complex. This is the firstoccurrence of bedded chert of that age inthe Tethyan regions;

(ii) a volcanic event is dated as Triassic;

RADIOLARIAN BIOSTRATIGRAPHIC DATA 237

(iii) bedded chert horizons are dated as Liassic;(iv) thick turbiditic sequences have been div­

ided into a number of units of Middle andLate Jurassic age.

We thank Dr. Hilal Bin Mohd Al-Azry (Ministry ofPetroleum and Minerals of Oman) for his support.The present work was financially supported by theBureau de Recherche Geologique et Miniere, Orleansand the Centre National de la Recherche Scientifique,Paris (CNRS-URA 705, GRECO n0088 and ASPEVOL. n06374 R11). We thank A. H. F. Robertson(Edinburgh), C. Blome (USGS, Tulsa, Oklahoma),E. A. Jr. Pessagno (UTD, Texas) and R. W. Scott(Amoco Prod., Oklahoma) for their valuable com­ments on the manuscript. Special thanks are due toN. Kito (Paris) for his help with the work includinguse of the scanning electron microscope.

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