REVUE DE MICROPALEONTOLO(',IE Vol. 41, n ° 1, mars 1998, pp. 71~87

PSEUDODICTYOPSELLA JURASSICA N. GEN., N. SP., A NEW FORAMINIFERA FROM THE EARLY MIDDLE JURASSIC

OF THE MUSANDAM PENINSULA, N. OMAN MOUNTAINS; SEDIMENTOLOGICAL AND STRATIGRAPHICAL CONTEXT

PSEUDODICTYOPSELLA JURASSICA N. GEN., N. SP., UN NOUVEAU FORAMINIFERE DE LA BASE DU JURASSIQUE MOYEN

DE LA PENINSULE DU MUSANDAM (NORD DE L'OMAN) ; CONTEXTE SEDIMENTOLOGIQUE ET STRATIGRAPHIQUE

by Michel SEPTFONTAINE* and Jos6 Esteves DE MATOS* *

ABSTRACT. -- A. new genus of foraminil'era Pseudodictyopselht n. gen., type species P. jurassica n. sp. is described in the Middle Jurassic of the Musandam limestone Group in the Wadi Naqab section (North Oman Mountains). Its trochospiral coiling and the presence of a valvular tooth plate places the new genus in the family Valvuliuidae emended. The presence of exoskeletal hypodermic radial partitions in the marginal zone of the chambers is a new f~ature among the valwdinids and justifies the emendation of the family and the introduction of the new s~Lbt'amily Pseudodictyopsellinae. The new genus is associated with Spiraloconuhts sp. and Selliporella donzellii (dasyclad algae) in an inner shelf carbonate environment. This assemblage is dated as Early Middle Jurassic (Bajocian) in the Tcthyan realm. Pseudodictyopsella jurassica n. gen., n. sp. occurs higher than the Early Dogger Timidonella - rich storm layers of the sections in Wadi Hagil and Wadi Naqab. The later genus was previously described as "Orbitammina" in several locations of the S. Musandam area.

Pd~SUMI~. -- Un nouveau gcnrc dc foraminif~rc Pseudodictyopsella n. gen., esp~ce type P. jurassica est d6crit dans le calcaire du ~,~'oupc de Musandam (Jurassiquc moyen) dans la section du Wadi Naqab. Son enroulement trochospiral6 et la pr6scnce d'nne dent valvnlairc pcrmcttcnt de placer ce nouveau genre dans la famille des Valvulinidae 6mend6e. La pr6sence d'~m r6seau hypodermique duns la zone marginale des loges est un nouveau caract~re dans cette famille et justifie son 6mendation ainsi que I'introduction de la nouvcllc sons famille des Pseudodictyopsellinae. Le nouveau genre est associ6 h Spiraloconulus sp. et Selliporella donzellii (dasycladac6e) daus un environnemeut de plate fbrme interne. Cet assemblage est dat6 dn d6bnt du Jurassique moyen (Bajocien) dans le domaine t6thysien. Pseudodictyopsella jurassica n. gen., n. sp. est observ6e au dessus de niveaux de temp~tes riches en TimidoneUa (base du Jurassique moyen) dans deux localit6s, les Wadi Hagil et Wadi Naqab. Le genre Timidonellu 6,tait d6crit pr6c6demment sons le nom d'Orbitammina daus plusieurs localit6s du Musandam.

Key-words: Foraminil'ers - PseudodictyopseUa n. gen. - Middlc Jurassic - Oman.

Mots-cl6s : Foraminif~res Pseudodictyopsella n. gen. - Jurassique moyen - Oman.

IN T ROD UCT ION AND HISTORICAL REVIEW

D u r i n g a r e c e n t s t u d y o f t i le J u r a s s i c of W a d i

N a q a b (de M a t o s , in p r e p . ) a n e w g e n u s o f f o r a m i -

n i f e r a w a s f o u n d in t h i n - s e c t i o n s o f t h e D o g g e r of

t h a t w a d i . T h i s s t u d y d i s c u s s e s t h e t a x o n o m y , p h y -

l o g e n y a n d c h a r a c t e r i s t i c s o f t h e n e w g e n u s Pseu- dodic tyopse l la ( t y p e s p e c i e s P. j u r a s s i c a n . s p . ) as

wel l as i ts s t r a t i g r a p h i c r a n g e a n d a s s o c i a t e d b i o t a .

T h e l i t h o l o g y a n d s e q u e n c e s t r a t i g r a p h i c i n t e r p r e -

* Geological Museum, UNIL-BFSH2, CH-1015 Dorigny/Lausanne, Switzerland. ** Abu-Dhabi Company for Onshore Oil Operations (ADCO), P.O. Box 270, Abu Dhabi, UAE.

72 JURASSIC FORAMINIFERA OF OMAN

tation are included together with an interpretation of its paleoecology and depositional environment.

The first to give an account of the geology of the Oman Mountains was Lees (1928), who mea- sured ca. 1438m of a combined Cretaceous and Jurassic carbonate section.

Hudson and Chatton (1959) presented a compre- hensive stratigraphic study of the Mesozoic of the Musandam Peninsula. They divided the Jurassic into seven units (a-g) based on micro- and macro- fossils. They also compared the Jurassic of the Musandam area with that of Saudi Arabia, SW Iran and Qatar.

Allemann and Peters (1972) reported a study south of Wadi Naqab near Habhab. They briefly described a carbonate Jurassic section, approxima- tely 1 100 m thick, that contains subtidal lime- stones and supratidal dolomites with algal mats and mud cracks. Later, Allemann and Schroeder (1972) made a biostratigraphic study of that section and introduced the new genus Spiroconulus (renamed Spiraloconulus), type-species S. perconigi, from the Early Dogger.

The classic synthesis of Glennie et al. (1974) gives a key to the understanding of the geology of the Oman Mountains and was a basis for further research. In this work, four microfossfl zones were defined in the Jurassic of the Oman Mountains and a Jurassic section was measured between Wadi Naqab and A1 Khatt village.

The paper by Ricateau and Rich6 (1980) was written as an explanatory note to accompany the geological map of Musaudam by Biehler et al. (1975). It contains definitions of formations, how- ever, which are not easy to follow in the field. Consequently they have rarely been used.

Later studies by Hughes Clarke (1988) and Glennie (1995) have contributed to a better under- standing of the geology of the area. On the other hand, the evolution and configuration of the plat- form margin in northern Oman, from Early Jurassic to Early Cretaceous, is especially discussed by Pratt and Smewing (1990, p. 82, fig. 10) and Rabu et al. (1990).

The overall study from which the present paper has been derived has recently resulted in three reports dealing with the Jurassic of the Emirates. De Matos (1994) presented a detailed biostratigra- phic and sedimentological interpretation on the Up- per Jurassic and Lowermost Cretaceous succession in the subsurface of Abu Dhabi. De Matos and Hulstrand (1994) give details on the Late Jurassic palaeogeography, depositional sequences and regio-

nal correlations of formations in Abu Dhabi. This study emphasizes the role of erosional truncations within the Late Jurassic sedimentary pile in U.A.E and Oman. De Matos et al. (1994) include results concerning the Early Jurassic biostratigraphy and sedimentation of Wadi Naqab, below the beds containing Pseudodictyopsella jurassica n. gen., n. sp. This study, by comparison with the subsurface of Abu Dhabi, demonstrates that much of the Liassic is most probably represented by a period of non deposition over the major part of the subsurface of Abu Dhabi.

L O C A T I O N AND G E N E R A L S T R A T I G R A P H I C A L S E T T I N G

The Wadi Naqab reference section is located in the northern Oman Mountains ca. 16 kin southeast of Ras A1 Khaimah, United Arab Emirates (Fig. 1). The section is situated between ca. 25°42 'N, 56°03 'E and 25°44 'N, 56°09 'E. The beds which yielded the new foraminifera PseudodictyopseUa ju- rassica n. gen., n. sp. crop out approximately two kilometers from the entrance to the wadi.

The area of study is within the largest basin of the Arabian shelf, the Rub'al-Khali basin, which was developed as an intracratonic sag in the Early Paleozoic (Beydoun, 1991). Published geological maps of this area include the 1 : 500 000 sheet of Glennie et al. (1974) and the 1 : 1 0 0 000 sheet Musandam Peninsula of Biehler et al. (1975).

The Wadi Naqab valley exposes a Triassic through Lowermost Cretaceous cyclic succession of shallow marine carbonates that is structurally little disturbed. The beds dip about 30 ° to the West. The total thickness of Jurassic beds is over 1310 m.

The Liassic sediments are represented by a do- minantly peritidal succession of metre-scale carbo- nate cyclothems punctuated by paleokarsts and hardgrounds (de Matos et al., 1994) resulting from oscillations of sea level.

During the Late Liassic the sea flooded large areas of the Arabian Peninsula; however a large part of the Toarcian and all Aalenian sediments are probably missing in the Musaudam Peninsula and in the subsurface of the Enfirates as well as in Saudi Arabia (Powers et al., 1966 ; Manivit et al., 1990, p. 14). In Qatar and Abu Dhabi wells, the Middle Jurassic carbonates directly overlie the Triassic. The succeeding sea-level rise led to more widespread carbonate sedimentation, but western

SEPTFONTAINE and DE MATOS 73

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74 JURASSIC F O R A M I N I F E R A OF OMAN

onshore and offshore A b u Dhab i r ema ined emergent unt i l deposi t ion of Ba joc ian sediments ( Izhara Fo r - ma t ion in this area) . The lower ha l f of this Fornm- t ion in the subsurface of Abu D h a b i is cons idered to be a t ime equivalent to the Jurass ic beds of Wadi Naqab , which yie lded Psendodictyopsel la j t t rass ica n. gen., n. sp.

In offshore Abu Dhabi the microfossi l associat ion of the uppe rmos t I z h a r a (time equiva len t of the beds d i rec t ly overlying Pseudodictyopsel la jurass ica n. gen., n. sp. beds in Wadi Naqab) consists o f : Alzonella cuvill ieri BERNIER and NEUMANN, 1 9 7 0 , Conicopfenderina mesojnrass ica ?, Ever t icyc lammi- n a s p . , H a u r a n i a deserta , Naut i locul ina oolithica, Paleopfender ina? sp. , Riyadhoides mcclurei (RED MOND, 1 9 6 5 ) , Redmondoides sp. of p re sumab ly Late Ba joc iau to Ea r ly Ba thon ian age. Below this assemblage the presence of Timidonella s a r d a BAS- SOULLET, CHABRIER and FOURCADE, 1974 points to an E a r l y Dogger age (de Matos, in prep . ) .

In Saudi Arab i a the Dhibi Limestone, t ime equi- va lent of the top uni t of the I z h a r a Fo rma t ion y ie lded the following f o r a m i n i f e r a : Conicopfende- r ina mesojurass ica (MAYNC, 1 9 7 2 ) , Hauran ia des- er ta HENSON, 1 9 4 8 , Lenticul ina sp. , Lingulina sp. , Naut i locul ina oolithica MOHLER, 1 9 3 8 , Paleopfen- derina sp. , Pseudomarssonel la m a x i m a REDMOND, 1 9 6 5 , Trocholina sp. This assemblage was assigned to the Late Bajoc ian (Manivit et al. , 1 9 9 0 , p. 1 5 7 , fig. 25 ) , a l though the p resence of C. mesojurass ica and Paleopfender ina sp. is a s ignature of a Batho- n ian age (Septfonta ine et al. , 1 9 9 1 , fig. 2) in Western Tethys. But the ident i f ica t ion of these two taxon is doubt fu l (Bassoullet , pe ts . comm.).

In the Musandam Pen insu la the " G r o u p c, U p p e r H a u r a n i a Limestones" of Hudson and Chat ton ( 1 9 5 9 ) , conta ining " O r b i t a m m i n a " (= Timidonella) in the basa l layers , a re most p r o b a b l y equivalent to the in te rva l of Wadi N a q a b that contains Pseu- dodictyopsella jurass ica n. gen., n. sp. (see s t ra t i - g raphic discussion below). The re is a good similar i ty

in the l i thological succession between the Ju rass i c section of Wadi N a q a b and the section s tud ied by [ ludson and Chat ton (1959 ) (Fig. 2). However our ch ronos t r a t i g raph ic i n t e rp re t a t i on is d i f ferent from the one of these au thors , according to the b ios t ra - t igraphica l a rguments discussed in the p re sen t pa- p e r : " G r o u p b, Lower H a u r a n i a Limestones" is Late Liassic and not B a j o c i a n ; " G r o u p c, U p p e r H a u r a u i a Limestones" is of Ba joc ian age a n d not Ba thonian .

Moreover , as es tabl i shed below, the genus Spira- loconulus (S. gigantetts CHERCHI and SCHROEDER, 1983 and Spiraloconulus sp.) is associated with P. jurass ica n. gen., n. sp. in a grea t p a r t of its s t ra t ig raph ic range in Wadi Naqab . The re fo re this in te rva l co r r e sponds (or is slightly younger ?) rou- ghly to the in te rva l of the H a b h a b section o f -Ea r ly Middle Ju rass i c age, where the genus Spiraloconulus (S. perconigi) was ident i f ied for the f irst t ime by Ai iemann and Schroede r ( 1972 ) .

L I T H O L O G Y A N D S E Q U E N C E A N A L Y S I S O F T H E B E D S C O N T A I N I N G P S E U D O D I C T Y O P S E L I A J U R A S S I C A N. G E N . , N. SP.

jurass ica n. gen., n. sp. (sample MUS-428) and its highest occur rence (MUS-485) is ca. l 1 5 m thick. I t is cha rae t e r i s ed by ca rbona te subt ida l cycles composed of shallowing - u p w a r d pa rasequences locally showing exposure fea tures (pa leokars t ) on top. In sub t ida l sections the sediment was most of the tinte submergent . Rare ly this type of cycle is capped by in ter - to sup ra t i da l sediments. In o r d e r to keep depos i t ion general ly within the sub t ida l zone, the ra te of sedimenta t ion shouht be less than or close to the ra te of subsidence.

FIG. 2. - Synthetic lithologs of sections in Wadi Naqab, Wadi Milaha, Wadi Bii~ and Wadi Hagil plotted in a timc-stratigraphic seale~ and proposed correlations between successions of foraminiferal assemblage-zones. The range of Pseudodictyopsella .jurassica n. gen., n. sp. is indicated. The succession of assemblage zones is in agreement with the biozonation proposed by Septfontainc (1984) in the Liassie - Early Dogger interval of Morocco and more generally with the biochronological scale presented by Septfontainc et al. (1991) for the

Jurassic of the Western Tethys. SB = Sequence Boundary.

Logs synth6tiques 6tablis d'apr6s des coupes gdologiques lev6es dans le Wadi Nuqab, le Wadi Milaha, le Wadi Bih et le ~hdi Hagil dans un cadre chronostratigraphique ; des corr61ations entre les assemblages de foramiuiJhres sont propos6es. L'extension stratigraphique de Pseudodictyopsella jurassica n. gen. est indiqude. La succession des zones d'ussemblages correspond h la biozonation propos6e par Septfontaine (1984) darts l'intervalle. Lias-Dogger inf. au Maroc et plus gdndralernent h l'dchelle biochronologique prdseutde par

Septfontaiue et al. pour le Jurassique de la T6thys occideatale. SB = Limite de s6quence.

S E P T F O N T A I N E and DE MATOS 75

-~ Wadi Naqab I S W ' : M ~ ~ d ~ i :ORMATION'~

( th is work)

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76 JURASSIC FORAMINIFERA OF OMAN

Five sequences (two of them are shown in Fig. 3) composed of several (commonly 4 to 5) parase- quences were recognised in this par t of the Jurassic section. A rhythmic succession of shallowing - up- ward limestone beds (parasequences) is obvious in the two basal sequences (1 and 2 in Fig. 3) where P s e u d o d i c t y o p s e l l a j u r a s s i c a n. gen., n. sp. is par- t icular ly abundan t . Several nodu la r limestone inter- vals are situated at the base of the parascquences . The top of sequence 1, above sample MUS-443 , is marked by a pa leokars t surface (K1), and such an emergence surface (K2) is also recognised 1,5 m below. This lat ter (K2) surface marks the b o u n d a r y between a thick bed of wackestone (with P. j u r a s s i c a

n. gen., n. sp.) and a th in-bedded in terva l of wackestones above. The in terval yielded E v e r t i c y -

c l a m m i n a sp., close to E. f r e q u e n s (MAYNC). P s e u -

d o d i c t y o p s e l l a j u r a s s i c a n. gen., n. sp. occurs in five horizons of sequence 1, contmonly at the top of parasequences (Fig. 3).

The holotype of P. j u r a s s i c a n. gen., n. sp. comes from sample MUS-444c , a pelletoidal packstone, also from the top of a parasequence included within sequence 2. This sample was collected imntediately below the maximum flooding surface (mfs) of this sequence. The new foramini fera is associated with S p i r a l o c o n u l u s sp. and M e s o e n d o t h y r a sp. It is also present towards the top of sequence 2 (sample MUS-451) in a pelletoidal and echinoidal wacke- stone. In sequences 4 and 5 (not shown on Text- fig. 3) P. j u r a s s i c a n. gen., n. sp. was recorded at the top of parasequences or within pelletoidal pa- ckstones of the transgressive system tract. The hi- ghest occurrence of P. j u r a s s i c a n. gen., n. sp. is in the deepest facies (i.e. area of the max imum flooding surface) of the sequence 5.

In conclusion most of the occurrences of P s e u -

d o d i c t y o p s e l l a j u r a s s i c a n. gen., n. sp are situated in subt idal sediments at the top of pa rasequences ; this foraminifera and other displaced particles are contemporaneous with the sedimentat ion. No traces of reworking of older sediments have been observed.

S Y S T E M A T I C P A L A E O N T O L O G Y

The generally accepted classification of forami- nifera has been established by Loeblich and Tappan ( 1 9 6 4 , 1988) . But this classification is considered to be unsat isfactory as it does not take into account the phylogenetic his tory of the taxonomic groups, here the htuolids larger tbraminifera . For tha t rea- son we prefer to use the classification of the Lituo- hds in t roduced by one of us (Septfontaine, 1988) based on morphological, s t rat igraphical and paleoe- cological cr i ter ia :

Order FORAMINIFERIDA EICHWALD, 1830 Suborder TEXTULARIINA DELAGE and

Ht~ROUARB, 1896 Superfamily LITUOLACEA de BLAINVILLE, 1 8 2 5 ,

emend. Septfontaine, 1988 Family VALVULINIDAE BERTHEL1N, 1 8 8 0 , emend.

Septfontaine, 1 9 8 8 , emend. (this work)

E m e n d e d d i a g n o s i s : Test t rochospiral ly coiled, generally tr iserial in ear ly stage, la ter may have an increased n u m b e r of chambers per whorl. Wall microgranular , rarely agglut inated; a keriotheca may be present . In te r ior of chambers simple or subdivided in the marg ina l zone by h y p o d e r m i c radia l par t i t ions . Aper ture in tc r iomargina l with a large valvular tooth simple or t ransformed. Trans- format ion may be as follows: presence of supple- men ta ry apertures (pores) on the va lvula r tooth plate with or without associated pil lars restr ic ted to the centra l axial pa r t of the test forming a columella-like s t ructure . The subconical pil lars (en- circling main aper tu ra l pores) are t r i angula r shaped in section, and related to a system of crosswise-obli- que stolons. A s iphon ma y be p resen t in the axial par t of the test. The p r imary aper ture is regressed in advanced forms and replaced by a multiple aper ture .

FIG. 3. - Detailed litholog, base of Wadi Naqab section, showing bed composition with foraminiferal and algal associations in the Early Middle Jurassic interval (samples De Matos 428* to 445) containing PseudodictyopseUa jurassica n. gen., n. sp. Beds arc arranged in shallowing - upward parasequences in a shallow - water lagoonal environment. They are grouped in subtidal sequences (1 and 2 are shown) of higher order, capped by paleokarstic surfaces (K1). Grainstone and packstone beds are interpreted as tidal or storm deposits,

often rich in foraminifera. 428* = FAD or First Appearance Datum; mfs = maximum flooding surface. Log d~taillE de la base de la coupe du Wadi Naqab montrant la structure de dEpOt des bancs et k'~s associations de JbraminiJ~res et d'algues ~t la base du Jurassique moyen (Echantillons De Matos 428* h 445) avec Pseudodictyopsdla jurassica n. gen., n. sp. Les bancs sont arranges en parasEquences $mersives dans art environnement peu profond de lagon. Ils sont groupEs en sequences subtidales (les sequences 1 et 2 sont moatrEes) d'ordre sup~rieur, se terminant par des surfaces palEokarstiqaes (K1). Les niveaux de grainstones et de packstones sont interprEt~s comme des depots de mardes ou de tempdtes, souvent riches en foramini~res. 428* = FAD ou premib~re

apparition; mfs - surJhce d~nondation maximum.

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78 JURASSIC F O R A M I N I F E R A OF OMAN

Subfami ly PSEUDODICTYOPSELLINAE n. subfam.

Diagnosis : Test t rochospi ra l ly coiled. Chambers subdiv ided by seconda ry ver t i ca l r a d i a l pa r t i t ions in a marginal hypodermal position. Wall calcareous microgranular with some agglutinated material. Aperture an umbilical interiomarginal slit, below simple valvular tooth plate. A siphon may he present in the axial part of the test.

Stratigraphic distribution: Middle Jurassic.

Genus P s e u d o d i c t y o p s e l l a n. gen.

Type species : Pseudodictyopsella jurassica n. sp.

Derivation of" name : This new taxon is morpho- logically closely related to Dictyopsella of Late Cre- taceous age; it has, however, a simpler inner structure and a Middle Jurassic occurrence, without phylogenetic relations with the latter. This is a justification of the prefix "Pseudo".

Generic diagnosis : Test t ree , t rochosp i ra l ly coi- led, with abou t 2 to 3 whorls. In t e r io r of chambers subdivided by vertical radial partitions in a sub- epidermal position. More rarely transverse parti- tions can be present. This exoskeletal microstructure is interpreted as a primitive hypodermic network. Wall calcareous microgranular, with some aggluti- nated material. Aperture an umbilical interiomar- ginal slit, below simple valvular tooth plate. An axial siphon may be present in some forms, as ancestral relict character.

Differentiation: This new genus can be easily d is t inguished t¥om Praekarnubia REDMOND, 1 9 6 4 because it lacks a columella in the cen t ra l p a r t of the test. Moreover , the va lvu la r tooth p la te of Pseudodictyopsella n. gen. is absent in Praekurnu- bia. The l a t t e r genus genera l ly shows an e longated t rochosp i r a l test while Pseudodictyopsella n. gen. has always a low conical test.

P L A T E 1

1 8. Psettdodictyol, sella jttrassica n. gen., n. sp., diverse non orientated thin sections in a pelletoidal paekstonc, sample Mus 444c, Wadi Naqab, Middle Jurassic Musandam Lime stone Group, SW Musandam Penins~fla, Ras A1 Khaimah (United Arab Emirates). Diverses sections non orient~es en lames minces dans un packstone h pelletoides. 1 : IIolotype, MGL 69482, deposited in the Geological

Museum of Lausanne (Switzerland), section parallel to the axis of coiling but laterally shifted; vertical radial partitions clearly visible, × 90. Section parall~le h l'axe d'enroalement l@$rement d~- calve latdralement ; les partitions verticales radiaires sont clairement visibles.

2 : Paratype, MGL 67703, section perpendicular to the axis of coiling, cutting through the last whorl composed of 2 to 3 chambers. Vertical radial parlitions are present in a subepidermal position, x 90. Section perpendicttlaire ~ I'axe d'enroulermmt cottpant it travers le dernier tour form6 par 2 ~t 3 loges. Lcs partitions verticales radiaires sont pr(~sentcs en position sous-@idermique.

3 : Paratype, MGL 67709, axial/oblique section with vet" tical radial partitions in the marginal zone of chambers, × 90. Section axiale/obliqtte montrant les partitions verticales radiaires darts la zone marginale ties loges.

4 : Paratype, MGL 67705, oblique section showing vertical partitions in the nmrginal zone oK the last chamber and the elliptical section of a siphonal nficrostructurc in the center of the test, × 90. Section oblique ntontrant les partitions verticales darts la zone margina~ de la derni~re loge et la section elliptique d'une microstructure siphonal~ au centre du test.

5 : Paratype, MGL 67704, vertical section subparallel to the axis of coiling, but laterally shifted; vertical par- titions visible in the first chambers only, not yet dcvc- loped in the last chamber, × 90. Section verticale sub-parall~le ~t I'axe d'enroulement, d~cal~e latdra~ment ; ~s partitions vertieales sont vi- sibles dans la premi$re loge settlement; elles ne sont pas encore d~velopp~es dans la dern~re lo~.

6 : Paratype, MGL 67703, tangential section cutting three chambers; vertical radial partitions visible with an horizontal subdivision in tile last chamber. This arran- gement in the marginal zone of the chambers is typical of a primitive hypodermic network, × 90. Section tangentielle recoupant trois loges ; les partitions verticales radiaires (lames) sont visibles ainsi qu'une subdivision horizontale (lamelle) dans la derni$re loge. Cet arrangement dans la zone margiaale des loges est typique d'nn r~seau hypodermique primit~f.

7 : Paratype, MGL 67710, tangential section cutting 2 chambers of the last whorl with vertical partitions in the marginal zone; two partitions, cut in their distal extremity, are restricted to the floor of the chamber showing a stalagmitic appearance, × 90. Section tangentielle recoupant deax loges du dernier tour avec des partitions verticales dans la zone mar- ginale ; denx partitions (lames) sont couples & leur extr(mtit(~ distale et montrent une Jbrme stalagmitiqtte.

8 : Paratype, MGL 67706, axial/oblique section; vertical partitions are present only within a chamber of the first whorl, x 90. Section axiale/obliqtte ; Ix~s partitions verticales sont pr~sentes seulenwnt duns les loges du premier tour.

SEPTFONTAINE and DE MATOS PLAT1

~EVUE DE MICROPAL~ONTOLOGIE, VOL. 41 , N ° 1

1.c 1.c.,, u

b

C

v. r. p.

g

f

0 , 5

m m

0

1

h.n.

v. r.p. e

h

. r .p .

J

FIG. 4 . - N o n - o r i e n t a t e d t h in sec t ions of Pseudodic tyopse l la j u r a s s i c a n. gen . , n. sp . , f r o m r o c k sample De Matos 4 4 4 c , Wad i N a q a b . 4 a : Ho lo type , axial / ob l i que sec t ion , s amp le De Matos 4 4 4 c = M G L 6 9 4 8 2 . 4 b - h : ob l ique / axial sect ions. 4 i - j : ob l ique a n d b a s a l / ob l ique sections. H y p o d e r m i c n e t w o r k visible in las t c h a m b e r of sect ion i. B a s a l sect ion = p e r p e n d i c u l a r to axis of coil ing, h . n. = h y p o d e r m i c n e t w o r k wi th t r a n s v e r s e p a r t i t i o n s ; 1.c. = las t c h a m b e r ; u = umbi l i cus ( and pos i t ion of the a p e r t u r e ) ; v. r. p. = ve r t i ca l

r a d i a l p a r t i t i o n s .

Sections non orient6es en lames minces de Pseudodictyopsel la jurass ica n. gen., n. sp. provenant de I~chantillon De Matos 444c , Wadi Naqab. 4 a : Holo type , sect ion axiale/obl ique, ~chant i l lon De Matos 4 4 4 c = M G L 6 9 4 8 2 . 4 b - h : sections axiales/obliques. 4 i - j : sect ions obliques et basales/obliques. Le rdseau h y p o d e r m i q a e est visible dans la derni$re loge de la sect ion i. Sect ion basale = p e r p e n d i c u l a i r e ?z l 'axe d 'enronlement , h. n. = r~seau hypodermique avec cloisonnettes transverses ; 1. c. = d e m u r e loge ; u = ombilic (et posi t ion de l 'oaverture) ;

v. r. p. = divisions radiaires vert icales .

SEPTFONTAINE and DE MATOS 81 ~ ~l.c.

v. rj p.

" "P" 1.c. ~ g

h 0,5 mm

0

FIG. 5 . - N o n - o r i e n t a t e d th in sect ions of Pseudodic tyopse l la j u r a s s i c a n. gen . , n. sp . , f r o m r o c k s ample De Matos 4 4 4 c , W a d i N a q a b . 5 a b : s u b a x i a l sect ions. 5c - i : t angen t i a l sect ions. 5 j : ax ia l /ob l ique sect ion. 5k-1 : b a s a l a n d ba sa l / ob l i que sect ions.

Sections non orient6es en lames minces de P s e u d o d i c t y o p s e l l a j u r a s s i c a n. gen. , n. sp. p r o v e n a n t de l 'dchanti l lon De Matos 4 4 4 c , Wadi Naqab .

82 JURASSIC FORAMINIFERA OF OMAN

The Cretaceous genus Dictyopsella MUNIER-

CHALMAS in Schlumberger, 1900 possesses a more complicated inner microstructure than that of Pseu- dodictyopseUa n. gen. It is characterised by nume- rous vertical radial and transverse partitions of several orders in a subepidermal position (inner margin of the chamber, exoskeleton). This micro- structure is called "hauraniiforme" or "choffatelli- forme" (when more complex and regular, like it is by DictyopseUa ) hypodermic network by Septfon- taine (1981) and is equivalent to the labyrinthic hypodermis of Banner (1970). Instead, the new Middle Jurassic genus Pseudodictyopsella n. gen. shows only vertical radial partitions (as in Prae- kurnubia) which are interpreted as elements of a primitive "kurnubiiforme" hypodermic network.

Pseudodictyopsella n. gen. differs from other valvulinids, like Siphovalvulina SEPTFONTAINE,

1988 and Paravalvulina SEPTFONTAINE, 1988 by the presence of an exoskeleton (the hypodermic network) which is completely lacking in the latter genera. PseudodictyopseUa n. gen. is also devoid of any endoskeletal microstructure (like pillars) such as occur in the pfenderinids.

Taxonomic and phylogenetic discussion: This new taxon clearly belongs to the valvulinids because of its trochospiral coiling and the presence of a valvular tooth-plate above the aperture. In some specimens (P1. 1, fig. 4 and PI. 2, fig. 2) a siphon- like microstructure, interpreted as the remnant of an ancestral character, may be associated with the tooth-plate in the axial part of the test. The presence of vertical partitions in the marginal zone of the chambers is interpreted as a derived, apomorphic feature among the valvulinids. The acquisition of an hypodermic microstructnre within this family is an exceptional evolutionary innovation. It can be compared with the episodic development of vertical radial partitions in the marginal zone of the cham- bers of pt~nderinids like the genus Pseudopfende- rina (BRUN, 1962) . This new character will appear in the valvulinids later in Cretaceous times, with more evolutionary success (in term of complication of the hypodermic network and of persistance through time), in the well known and widespread genus Dictyopsella. These facts point to a mode of iterative evolution within the family Valvulinidae.

P L A T E 2

1-5. Pseadodictyopsella jurassica n. gen., n. sp. in non - orientated thin sections of a pelletoidal packstone, sample Mus 444c, Wadi Naqab, Middle Jurassic Musandam Lime- stone Group, SW Musandam Peninsula, Ras A1 Khaimah (United Arab Emirates). Diverses sections non orientdes en lames minces dans an packstone it pelletoides. 1 : Paratypes, MGL 67704, axial/oblique sections sbowing

vertical partitions in earlier chambers, x 90. Sections axiales/obliques montrant des partitions ve t ticales dans les premieres loges.

2 : Paratype, MGL 67707, horizontal section through the 4 chambers of the last whorl. Vertical radial partitions are visible in the marginal zone and the section of tl~e axial siphon in the center of the test, x 90. Section horizontale ~t travers les 4 loges du dernier tour. Les partitions verticales radiaires sont visibles dans la zone marginale ainsi que la section du siphon axial aa centre du test.

3 : Paratype, MGL 67709, axial/oblique section through 3 chambers of the penultimate whorl and 1 chamber of the last whorl. Vertical partitions visible in all cham- bers, x 90. Section axiale/oblique it travers 3 loges de l 'avant dernier tour et 1 loge da dernier tour. Les partitions verticales sont visib~s dans toutes k s loges.

4 : Paratype, MGL 67703, horizontal/obhque section through 1 chamber of' the last whorl with about 12 vertical radial partitions in the marginal zone, x 90. Section horizontale/oblique it travers une loge du der nier tour avec environ 12 partitions verticales ra- diaires dans la zone marginale.

5 : Paratype, MGL 67704, axial/oblique section, some ver- tical partitions are visible in earlier chambers, × 90. Section axiale/oblique avec quelques partitions verti- cales visibh~s dans k s premieres loges.

6-7. Timidonella sarda BASSOULLET, CtUBRIER and FOURCADE, 1974, in a monospecific foraminiferal/pelletoidal grainstone deposited by tidal currents or storm waves. Wadi Hagil, Middle Jurassic Musandam Limestone Group, sample ST 1230, SW Musandam. Grainstone it JbraminiJ~res monosp6cifiques et peUetoides ddpos6s p a r un courant de mar~e ou une vague de temp~te. 6 Diversely orientated sections, two of them through the

plane of coiling and the macrospheric embryo, x 60. Sections d'orientations diverses, deux d'entre elles tra- versent le p lan d'enroulement et l 'embryon macrosph6- riqae.

7 Sections perpendicular to the plan of coiling showing endoskeletal pillars in the central part of the test, and some partitions of the hypodermic network, x 60. Sections peu~endiculaires au plan d'enroulement mon- trant les piliers de l'endosqaelette aa centre da test et qaelques partitions (lames) du r6seau hypodermique.

SEPTFONTAINE and DE MATOS PLATE 2

REVUE DE MICROPALEONTOLOGIE, VOL. 41 , N " 1

84 JURASSIC FORAMINIFERA OF OMAN

P s e u d o d i c t y o p s e l l a jurass i ca n. sp. (P1. 1, fig. 1-8 ; P1. 2, fig. 1-5 ; text-fig. 4-6)

Derivation of name: This new taxon is so far known only in Jurassic sediments.

Diagnosis : A small size species of the new genus Pseudodictyopsella n. gen. with about 3 whorls and 6 chambers in the last whorl. Sutures between chambers or successive whorls slightly depressed. General shape a low conical trochospire.

Holotype : MGL 69482 , an axial/oblique section (Fig. 4a and P1. 1, fig. 1) in a thin section of rock (sample MUS-444c) from the Middle Jurassic Mu- sandam Limestone Group, surface section in Wadi Naqab, SW Musandam Peninsula (Ras A1 Khaimah, UAE).

Material: 27 random sections in 10 limestone thin sections (registered as MGL 67702 to MGL 67710 and 69482 , Palsyst 1138) deposited in the Geological Museum of Lausanne (Switzerland).

Description: Test a low trochospire, irregular, conical or bowl shaped, with sutures between suc- cessive whorls slightly depressed. About 2 to 3 whorls with 6 chambers in the last whorl. Umbilicus ahuost closed. First chambers and proloculus not visible, but the latter is probably of the microsphe- ric type. The interior of the chambers is subdivided by vertical radial partitions in an hypodermic po- sition; more rarely some transverse partitions are present. These subdivisions appear very early du- ring ontogenic development of the test. They are visible inside the youngest chambers of the first whorl in several sections in Text-figures 4 and 5. Vertical partitions are also present in the last chanl- hers; they are visible in sections through the last whorl, perpendicular to the axis of coiling (Fig. 5k ; P1. 2, fig. 2). Their number is about 5 per chamber throughout the test, sometinms less; they are of variable length. Distal part of partitions (toward the center of the chambers) shows a stalactitic appearance in vertical sections as in the holotype Plate 1, fgure 1 (test oriented with the umbili- cal/apertural face upwards). Partitions are not straight but often irregular, slightly bent or thicke- ned in their central or upper part. These characters are typical of vertical partitions in an hypodermic network. The aperture is an interiomarginal slit at the base of the septum which is a flat and elongated tooth plate sometimes modified as a siphon-like microstructure in the axis of the trochospire (P1. 1, fig. 4 ; P1. 2, fig. 2). Wall calcareous microgranular with some agglutinated material.

tooth plate penultimate above aperture chamber

" " ' " " ~ . ; ~ ' i ' ,

/ ..

vertical radial partitions

FIG. 6. - Three-dimensional model of Pseudodic tyopsel la j u r a s - sica n. gen., n. sp. reconstructed from random thin sections (Fig. 4 -5 ) ; lateral/umbilical view, test slightly inelined toward

observer.

ModUle it trois dintensions de Pseudodictyopsella jurassica n. gen., n. sp. construi t it par t i r des sections non orient6es des Fig. 4 e t 5 ; r u e l a t d r a l e / o m b i l i c a l e , le tes t est l d g S r e m e n t

inclin6 vers l 'observateur.

Dimensions: Height of test : 0,3 mm (average). Diameter of the last whorl : 0,8 mm (average).

Locality and horizons of holotype and para- types : Wadi Naqab, Ras AI Khaimah, sample MUS- 444c (holotype); samples MUS-428 to 485 (paratypes).

Associated microfossils: This new taxon is cur- rently associated with the following assemblage: Amijiella amiji (HENSON, 1948), Everticyclammina sp., Haurania deserta HENSON, 1948, Mesoendo- thyra sp., Nautiloculina oolithica M O H L E R , 1938, Siphovalvulina sp., Spiraloconulus sp., S. giganteus CHERCHI and SCIIROEDER, 1983, Redmondoides l u g e o n i (SEPTFONTAINE, 1977).

Stratigraphic and geographic distribution: Wi- thin the stratigraphic interval containing Pseudo- dictyopsella jurassica n. gen, n. sp. in the Wadi Naqab section, we also observe the First Appearance Datum or FAD of the calcareous alga Selliporella donzellii SARTONI and CRESCENTI, 1962, which is indicative of a Bajocian to Bathonian age (Granier and Deloffre, 1993). This strongly suggests a Ba- jocian age for the stratigraphic interval containing P. jurassiea n. gen., n. sp. This is confirmed by the FAD of Redmondoides lageoni (the first occu- rence of this species is in the Early Dogger in the

SEPTFONTAINE and DE MATOS 85

Tethyan realm, Septfontaine, 1980) at the very top of the stratigraphic distribution of Pseudodictyop- sella jurassica n. gen., n. sp. This new taxon is presently known only in the Wadi Naqab area (SW Musandam).

Paleoecology and depositional environment : The associated microfossils indicate an environment of warm tropical waters in a shallow protected carbo- nate platform. The general sedimentary microfacies of pelletoidal wackestone/packstone point to a quiet water environment in an inner shelf position.

S E D I M E N T O L O G I C A L AND S T R A T I G R A P H I C A L D I S C U S S I O N IN T H E C O N T E X T OF T H E MUSANDAM P E N I N S U L A

The Musandam Group, introduced by Glennie et al. (1974), is a succession of shallowing -upward limestone beds arranged in sequences of different orders, metric to decametric, in a lagoonal to locally supratidal environment (see above and Text-fig. 2- 3). The bioclastic grainstone/packstone beds contai- ning foraminiferal tests in abundance (e.g. the Ti- midonella beds in Wadi Hagil, P1. 2, fig. 6-7) are interpreted as accumulations of floated empty shells displaced by tidal currents or storms waves. An Early Jurassic example of storm layers with orbi- topsellids is given by Septfontaine (1985) in Mo- rocco ; for a recent equivalent in Tunisia see Davaud and Septfontaine (1995).

By contrast, most foraminifera observed in sub- tidal mudstone/wackestone beds in the Jurassic of the Musandam group, are in a relatively autochtho- nous position. This is due to the protected (from waves and tides) environment of their inner-lagoonal habitat. Moreover, no indications of important emer- gence (with erosion of paleorelief and clasts accu- mulation) of previously deposited formations have been recorded in the Middle and Upper Jurassic of the Musandam Peninsula.

In this situation, reworking of older assemblages is improbable ; the succession of foraminiferal as- semblages in Fig. 2 reflects a sequence of bioevents (assemblage zones)which are in agreement with the general biostratigraphic scale proposed by Scptfon- taine et al. (1991) for the margins of the Western Tethys.

New taxonomic data, discussed below, lead to a reappraisal of the biostratigraphic scale in the sou- thern area of the Musandam Peninsula (Fig. 2).

This is necessary to confirm and precise the stra- tigraphic position of Pseudodictyopsella jurassica n. gen., n. sp. in the Early Dogger. It concerns the biostratigraphic succession of the larger foraminife- ra assemblages presented by Iludson and Chatton (1959, fig. 3) and Allemann and Peters (1972, fig. 4) which include the well known "Orbitammina elliptica" d'ARCHIAC, 1843 index microfossil of Late Bathonian age. During a previous field party in the year 1991 organized with the Ministry of Oil and Industry (Muscat, Oman), the Mineralogical Insti- tute of Bern (Prof. T. Peters) and the Geological Museum (Lausanne), the beds containing abundant "O. elliptiea" (storm layer) at the entrance of the Wadi Hagil were resampled by one of us (M. Sept- fontaine) and this taxon definitely identified as Timidonella sarda BASSOULLET, CHABRIER and FOURCADE, 1974 of Early Dogger age (Late Aale- nian to Early Bajocian, Septfontaine et al., 1991). This confirms the absence of the Meyendorffina-Or- bitammina group on the Arabian carbonate plat- form and more generally in the S-Tethyan realm as already stated by Bassoullet et al. (1985).

As a consequence, this important marker interval containing T. sarda in Wadi Hagil is now placed in the Early Dogger (probably Early Bajocian) instead of Late Bathonian. In Wadi Naqab, the Timidonella

- horizon is situated ca. 290 m above the sole ammonite found by one of us (J.E. de Matos), which is most probably a Bajocian Poecilomorphus occur- ring in the lower half of the Humphriesianum zone, Early Bajocian (M. Howarth, pers. comm.). These new taxonomic and biostratigraphic data yield sup- plementary arguments which permit to precise the stratigraphic position of the new genus Pseudodic- tyopsella :

1. In Wadi Naqab the first occurrence of Pseu- dodictyopsella jurassica n. gen., n. sp. is 27 m (sample 420) above the TimidoneUa - horizon which is situated between Late Aalenian and Early Bajo- clan in Morocco (Septfontaine et al., 1991). It follows that P. jurassica n. gen., n. sp. appears probably during the Bajocian in the Musandam area.

2. The extinction of P. jurussica n. gen.o n. sp. is in the Bajocian as indicated by its association with Selliporellu donzellii and the FAD of Redmon- doides lugeoni.

3. The new genus Pseudodictyopsella is currently associated with the genus Spiraloconulus spp. (S. giganteus and Spiraloconulus sp.) along a large part of its range. The later" genus (species S. perconigi) is often found associated with the Timidonella-Gut- nicella assemblage (Aalenian-Bajocian) in Western

86 JURASSIC FORAMINIFERA OF OMAN

Tethys (Septfontaine et at., 1991). The association of Spiraloconulus (S. perconigi) with Gutnicella was already reported by Allemann and Schroeder (1972) in the southern Musandam (A1 Fujairah Emirate).

In conclusion the occurrence of Timidonella sar- da and Pseudodictyopsella jurassica n. gen., n. sp. in the Musandam peninsula is in the Bajocian. These two taxa appear successively in the Wadi Naqab section and their ranges do not overlap.

ACKNOWLEDGEMENTS

Especial gratitude is given to R. Hulstrand and Julieta de Matos for assistance and continuous sup- port during the measuring and sampling of the section of Wadi Naqab. Thanks are expressed to H. Mueller (ADCO) for constructive discussions and suggestions concerning the sequence stratigraphic interpretation and to M. Howarth (British Museum) for the ammonite identification.

We thank the Ministry of Oil and Industry (Mus- cat, Oman), the Prof T. Peters (University of Bern) for technical help in the field, and the Geological Museum of Lausanne and its Director, A. Baud, for encouragement during this study. Early drafts of the manuscript were reviewed by H. Mueller and K. Glennie and their comments are gratefully ac- knowledged.

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