Permian to Cretaceous radiolarian biostratigraphic data from the Hawasina Complex, Oman Mountains P. DE WEVER 1 Ch. BOURDILLON-de GRISSAC 2 & F. BECHENNEc 3 1 CNRS UR 1315, Universite P. M. Curie, T 15-16 E4, F-75252 Paris Cedex 05, France 2 BRGM-SGN-GEO, F-45 060 Orleans, France 3 BR GM, 10 Rue Picheri, 44300 Nantes, France Abstract: The analysis of foraminifera and radiolaria in 3000 carbonate and 150 siliceous rock samples from the Oman Mountains results in revision of the existing stratigraphy and supports the definition of new units. In the Hawasina allochthonous unit the main results are as follows: (i) Permian bedded chert exists near the base of the sequence and is thus the first Permian bedded chert occurrence reported from the Tethyan region); (ii) an important volcanic event is dated as Triassic; (iii) bedded chert horizons are dated as Liassic; (iv) the thick turbiditic sequence has been divided into several units of Middle and Late Jurassic age. In the Samail ophiolite: (i) the ages of four tectonic episodes were established from the beginning of oceanic spreading (Albian-Early Cenomanian), to the obduction of the ophiolitic nappe (Campanian). Around 3000 limestone and chert samples were collected for palaeontological analysis during the BRGM mapping project (1/100000) in the Central Oman Mountains. Carbonate rocks yielded foraminifera, ostracods, algae; also macrofauna; while the siliceous rocks yielded identifiable radiolarians. Radiolarians were extracted from rock samples with established techniques (De Wever et al. 1979b; 1982b) that use extremely dilute hydrofluoric acid (1 to 0.1%), and successive etching. The ages of samples were established using different sets of data handled by micro- computers. (Vrielynck & Granlund 1988, Vrielynck 1989) and from published biozona- tions or unpublished data (Pessagno 1977; De Wever et al. 1979a; Baumgartner et al. 1980; De Wever, 1981a,b,c, 1982 a,b; Blome, 1983; Baumgartner 1984, 1987; De Wever & Micon- net, 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 et al. 1984, 1987). For each species we used the range of its acrozone, and for each sample we used the concurrent range zone. Geological setting The Oman Mountains comprise an arcuate chain (700 km long x 50-140 km wide), from the Musandam Peninsula in northwest to the Sur region in the southeast (Fig. 1). The mountains culminate in the 3000 m high Jabal Akhdar and are flanked to the north by the Gulf of Oman or by the Batinah plain, and to the south by the deserts of interior Oman. The mountains were uplifted mainly during Mio-Pliocene. The following main units are recognized from the bottom to the top: Upper Proterozoic crys- talline basement in the southeast (Jabal Ja'alan and Qahlat region); the 'A autochtonous unit', transgressive on the basement, this comprises volcanic and sedimentary rocks, deformed during late Panafrican and Hercynian orogenic events; and the 'B autochtonous unit', mainly composed of transgressive carbonates dated as Permian to Cretaceous. The carbonates were deposited on the northeast edge of the Arabian platform and were deformed and locally meta- morphosed during the Eo-alpine orogenesis; the Hawasina nappes are composed of mainly deep-water sedimentary and volcanic rocks of Permian to Cretaceous age. They represent a fragment of the passive margin of the Southern Tethys that was overthrust onto the Arabian platform during Late Cretaceous time. The Samail ophiolite formed during Albian, Ceno- manian to Senonian times (De Wever et al. 1988b), and was also obducted onto the Arabian platform during Campanian- Early Maastrichtian time (Beurrier et al. 1987). The 'Neo-Autoch- thonous unit' is transgressive on all the previous units. Sedimentation began during Middle to Late Maastrichtian and continued until Miocene time (Burdigalian). The eastern and central outcrops 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 225-238 225
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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
225
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(:-_::-:"/-1 Homrot Duru Group
ill AI Aridh Group
•Umor Group
40 km7 ! I I I
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Fig. 1. Location map of the area studied (Central Oman Mountains). a Location map; b Simplified map of part of the Oman Mountains (after Bechennec, 1987),showing the main outcrops of the AI Aridh, Hamrat Duru and Umar Groups
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
HAMRAT OUR U G R 0 U P
F NEOCOMIAN
NEOCOMIAN
NEOCOMIAN
J:0 No>=
NEOCOM IAN «z
TITHONIAN ~R KIMMERIDGIAN .er
MV 493 R 9R
U1fB 288B
~DJ 359E
«N>-«3:;:)t?
--- --
J:t-«CDt-«~
F(RwF)
F(RwF1
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R RwF PF
RRRR
SENONIAN
TURONIANCENOMAN.
L.ALB.CENOM
Calp TITHONIAN
lIASSIC· DOGGER
TRIASSIC(oHw PERMIAN)
Up/
TRIASSIC
TRIASSIC
PERMIAN
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
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
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.;
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
~--------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.
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")
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)
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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