Biostratigraphic zonation of Bathonian-Callovian rocks from Gebel El-Maghara Northern Sinai, Egypt

Journal of African Earth $cienco, Vol. 13, No. 2,.183-192, 1991. Printed in Groat Britain

0899-5362/91 $3.00 + O,00 © 1991 Pergmmm Press ptc

Biostratigraphic zonation of Bathonian.Callovian rocks from Gebel EI-Maghara Northern Sinai, Egypt ADELA. ABD~I.~H~AB Deparcnentof Geology.Facultyof Science,AssiutUniversity,Egypt (Accepted for publication 24th November, 1990) Abstract - The Bathoni~m-Callovisn rocks of EI-Maghara have been subdivided into seven biostratigraphic zones mainly based on their brachiopod fauna. The internal slructures of the well preserved bmchiopoda have also been elucidated.

INTRODUCTION

The well known Jurassic outcrops in Northern Sinai have been the subject of several stratlgraphical studies, cf. Douvillg and Barthoux (1913); Douvill~ (1916); Farag (1957); Said and Barakat (1958). Recently, EI-Far (1966} classified the EIMaghara section which attains a thickness of 1900 m, into several llthostratlgraphic units from base to top as: Mashabba Formation, RaJabiah Formation, S h u s h a Formation, Bir Maghara F o l m a t i o n , Safa F o r m a t i o n a n d MasaJid Formation. M

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Brachiopods and molluscs have been collected and identified from Bathonian-Callovian success/on of the Gebel El-Maghara section and have been used as a tool for biozonation. The well preserved brachiopoda specimens were examined microscopically using transmitted light by the method of acetate peels (Abdalla Hegab, 1984}. The microscopic examination covered a study of the inner skeletal elements.

calations rich in Ostrea sp., few corals and rare Praecyclothyris bogoslovskil Makridin; yellow calcareous marls with thin limestone intercalations containingrare specimens belonging to the genus Eudesla King, Septallphor~a Jakovlevt M a k r l d l n , S. sobolevl M a k r l d l n , Zeillerta doneziana Nalivkin and Natlca sp., thin alternations of clayey limestone and mudstone rich in Ptyctothyrls dorsopllcata Suess, buff, yellow glauconiUc limestone with m u d s t o n e intercalations, calcareous marls rare in Ostrea sp., Russirhynchla flscheri fischerl Roufll.,

Rhactorhynchia plnguls ukralnlca Markidin and Praecyc/othyr/s bogos/ovsk//Markldln; calcareous mudstone rich in Eudesia King, Russirhynch~a Jlschert Rouill, Rhactorhynch/a p~r~guis ukralnlca M a k r i d i n a n d r a r e in Eligmus sp. a n d

Gryph~el'~nus Jabbokensts Lewy and smooth Terebratulida, marly limestone with mudstone intercalations, cavernous limestone, oolitic marly limestone, massive mudstone, clayey limestone, marly limestone, calcareous shales, compact sandy and silty shales and claystone, hard limestone, calcareous shale and claystone, white limestone, reddish shales and claystone rich in Rhynchone/la sp., R. mascl//dens/s, and rare Praecyc/othyr{s and hard calcareous mudstone.

8TRATIGRAPHIC FRAME'WORK The Middle Bathonian-Callovian succession (221 m thick) exposed in Gebel EI-Maghara (Fig. 1) could be detailed as follows from top to bottom: MmmJ~ Fmnmatloa Ordy the lower 148.5 m are exposed in the area studied. They belong to the Kehailia Member and are composed from top to bottom of calcareous mudstone and claystone rich in Lobo/dothyr/s sp.; nm-~sive limestone with thin mudstone inter-

Safl F o rmatio n (72.5 m thick) The formation consists from top to bottom of flinty limestone, marly shales, sandy shales rich in Septa/fphorfa sp. and Ostrea sp., clayey sandstone, marly shales with rare Ostrea sp. and fossil fragments, hematitic shales with rare Rhynchonella sp. and Septaltphoria Jakovlevl Mak rld ln , oolitic m a r l y l i m e s t o n e rich in Septallphoria sobolevl Makridin, Ivanoviella arcuata Rouill., and rare in Septa//phor~ sp. and Ostrea sp., greenish hematRic shales rich in

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m thick). This zone is overlain by Septa/tphor/a sobolevi/IvanovieUa a r c u a t a zone a n d underlain by continental sandstone and shale facies. It is characterized by yellowish green hematitic shale and rich m Rhactorhynch/a osco/tca Makridin, Praecyclothyrts moeschi donetzlana Makridin, Septal(phorla sobolevi Makridin and S. Jakovlevi Makridin and having rare Ostrea sp. and smooth Terebratulidao

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2- Septaliphoria sobolevi /Ivanoviella arcuata zone (3 m thick)~ It is overlain by Septa/Iphor/a sp. / Ostrea sp. zone and underlain by Rhactorhynchia oscolica/Praeo

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cyclothyrts moeschi donetzlana / Septallphoria sobolevi zone. This zone is characterized by oolitic marly limestone rich in SeptoAtphor/a sobolevi Makridin and Ivanov/e//a a r c u a t a Roll. and rare in Ostrea sp. Septaliphoria jakovlevi Makridin, S. pectunculoides (Etall.), Rhynchonella loxiae Fischer and Rhynchone//a sp. 3- Septal!phorla sp./Ostrea sp. zone (5 m thick). This zone is overlain by Rhynchtxwlla masqfldensis zone and underlain by Septaliphorla sobolevi/ Ivanov/e//a arcuata zone. It is formed of grey sandy shale rich in Septa/tphorta sp. and Ostrea sp. 4- Rhynctwne//a mast!//der~s zone (4 m thick) It is o v e r l a i n by E u d e s i a / R u s s i r h y n c h i a / Rhactorhynchi z o n e a n d u n d e r l a i n b y Septa//phor/a s p . / O s t r e a sp. zone. This zone consists of reddish yellow shale and claystone and is r i c h in Rhynchonella masaJidensis a n d Rhynchonella sp. and rare in Praecyclothyrts.

irsg.I Indexmap ~xnvlngthe lotmUonofGebe! EI-Maghara, NorthernSmal.

5- Eudesla/ Russirhynchia / Rhactorhynchlazone

stones, fissileshales, cross-bedded sandstones, friable shales, cross-bedded sandstone.

jabbokensis Lewy. 6- Ptyctothyris dorsoplicata zone (20 m thick). It

{10 m thick). This zone is overlain by Ptyctothyris Rhactorhynchla oscolica Makridin, Praecyclo- dorsoplicata zone and underlain by Rhynchonella t/~rts n m e s c h / ~ Makrldin. and Septa/i- mastg/densts zone. It is formed of hard, massive, ptm¢~ sobo/ev/ Makrldln and rare in smooth yeUowish grey, c a l c a r e o u s m u d s t o n e rich in Terebratulida, friable shales with iron Eudesla sp., Russlrhynchiaj'Lscheriflscheri Roufll. concretiolm, compact unfossfllferoussandstones. and Rhactorhynch~ pinguis ukraintca Makridin coral beds, sandstone, shales, cmssbedded sand- a n d rare m Eligmus sp. a n d Gryphaeligmus

]M~glM~mll~bdic sonaUon (Fig. 2) The Bathonlan-Callovian succession exposed at Gebel EI-Maghara n e a r the coal mine has been subdivided into seven biozones from top to base as follows:7- Lobo/dothyrts sp. zone 6- P t y c t o ~ dorsoplleata zone 5- Zudesla/ Russ#'hynchla/ Rhactorhynchiazone 4- R h y n c ~ masqJ/densts zone 3- Septa/tptwrla sp./Ostrea sp. zone

2- Septaltphtrfa sobolevg lvanovtella arcuo_t~ zo n e I -Rhactorhy~hla/Prae~clothyrls/Septai!p~ zone

• 1- Rhactorhynchia oscolica/Praecyclothyris moesch/donetz/ana/Septa/tphor/a sobo/ev/zone (4

is overlain by Lobo/dot/hyrts sp. zone a n d underlain by Eudesla/Russirhgrichia/Rhactorhyncl'da zone. This zone is characterized by a n alternation of dark grey to buff clayey limestone a n d pale grey calcareous m u d s t o n e and claystone. It is rich in Ptyctothyr/s dorsop/tcata Suess. 7- Lobo/dothyrts sp. zone. The h a r d compact, g r e y i s h c a l c a r e o u s m u d s t o n e b e l o n g i n g to Kehailia Member is rich in the smooth Terebratulida Lobo/dothyrts sp+ P ~ ! ~'~OENVIRONMI~-NT

The environmental conditions prevailing during the deposition of the Sara Formation can be subdivided into two phases:

Biostratigraphic zonation of Bathonian-Callovian rocks from Gebel El-Maghara Northern Sinai, Egypt

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ADELA. ABD~LAHEGAB

186

the lower two thirds of a thick alternating shales and s a n d s t o n e s sequence are non fossiliferous and are characterized by primary depositional structures, such as cross-beddlngs and plant remains of continental probably fluviatfle origin. These sediments, usually ferruginous, are characterized by brown or red colouration. They can be explained by the regression of the sea water permlting rivers a n d s t r e a m s to deposit fluviatfle sediments; the u p p e r third of the Sara Formation is characterized by shallow marine facies, consisting of marly limestone, oolitic limestone and marly shales. This refers to the beginning of a transgressive phase. The shore line of this transgression is marked by coralline limestone with coral heads. The faunal assemblage of this part (brachiopoda, mollusca, coral and rare echinoderms) support deposition in shallow marine condition. The energy condition of the water in this part of the Sara Formation was slightly to intermittently agitated. The presence of oolites in the limestone supports this fact. The flinty limestone (top of Safa Formation) is considered as a marker-bed, topping the Sara Formation in the Maghara dome. MasaJid Formation is m a d e up of thick shallow marine sediments. These sediments are mostly composed of marly limestone, calcareous mudstone, marls and shales. The lower part of the MasaJid Formation (Kehailia Member) is very rich in macrofauna, especially Rhynchonellida and Terebratulida and is characterized by dominant clastic facies, composed of shales, claystones and m u d s t o n e s in addition to few marls and marly limestones. This facies was deposited n e a r the continent and was carried by rivers and streams more or less to the shore. S U B S T R A T A AND FEEDING

The high delormatlon of the fossil assemblage which is embedded in the greenish shale (bed No. I I) at the marine base of Safa Formation might be due to adequate diet that stimulated competition amongst the Rhactorhynchia, Praecyclothyrts and Septa//phorta (Makridin, 1964). The high diversity of Eudesia, and the presence of Gryphaeligmus Lewy in calcareous m u d s t o n e (bed No. 32) might also suggest that the nature of the substrata was rather favourable for these brachiopods. Furthermore, the presence of large size Rhynchonellida and Ptyctothyrts in the yellow shale and the calcareous m u d s t o n e might refer to suitable substrata and sufficient food. Changes in the frequency of the occurrence ol Septaliphoria sobolevi Makrldin and S, jakovlevi

Makridin is subjected to changes in the nature of the sediments. The highest occurrence frequency in the Safa Formation was found in the greenish shales while this frequency decreases gradually towards the oolitic m a r l y limestone a n d the hematitic yellow shale. Surprisingly, it is observed that only the size of Septaliphoria sobolevl Makridin decreases from bottom to top. SYSTEMATIC DESCRIPTION

Here are the classification and description of some well preserved brachiopoda giving the internal skeletal elements in order to interpret the ontogenesis of each species. Order RHYNCHONELLIDA Moore, i952 Superfamfly Rhynchonelloidea Gray, 1848 Family RIIYNCHONELI,IDAEGray, 1848 Subfamily Rhynchonellinae Gray, 1848 Genus Septaliphoria Leidhold, 1921 Septaliphor~a soboIevi Makridin, 1964 'Fig 4)

Terebratula tacur~osa Gorov. 1869, p. 47 Septaliphoria lacunosa Makridin, 1952. p. 50, pl. ),1. fig. 3, pl. I l l , figs 1~3. Right dental plate thin. slightly curved; crura hook shape; teeth massive; socket floor deep and concave laterally: o u t e r hinge plates strong, slightly c u r v e d

Septaliphoria pectunculoides (Etallon), 1861 ~Fig, 5)

Rhynchonella peclut~cuIotdes Etallon, 1861. p. 289, pl. 42, fig. 3. Ix)riol, 1874, p. 242: Nalivkin. 1910, p. 55: Rollier~ }917, p. 162. Rhynchonella pectuncula Etallon, 1862. p. 2 0 8 Rhynchonella pecumculoides Etall. var, Lor: Nalivkin. 1910, !), 52, pl. IV, figs.6, 7, RhynchoneIta pectunculoides Etall.Var.a: Nalivkin, 1910, p 55, Rhynchonella pectunculoides Etall.Var.b: Nalivkin, 1910, p. 56, pl, IV, Fig. 8; Makridin, 1952 p 79~ pl. VIII, figs, 4, 5: pl. IX, fig. Septaliphoria subtilis Makridin, 1952, p. 77, pl. VIII, fig. a,

Septaliphoria pectunculoides (Etalloni-Makridin, 1964, p. 102. pl |I~ VII1. fig. 3 Internal structure: Dental plates subparallel; teeth massive: socket floor wide and deep; crura radulffer; median septum long occupies about one third of the dorsal valve total height; septalium is deep: septalial plates are supported by median septum: deltidia[ plates well developed; outer hinge plates nearly straight,

Biostratigraphic zonation of Bathonian-Callovian rocks from Gebel EI-Maghara Northern Sinai, Egypt

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Fig. 3. Diagrams showing internal skeletal elements in Rhynchone//~[a A) a- ventral valve; b- dorsal valve, 1-dental plates, 2- o u t e r hinge plates, 3- crura, 4- septal plates, 5- m e d i a n s e p t u m , 6- tooth, 7- d e n t i c u l u m , 8- socket floor. B) Ventral valve : 1- dental plates, 2- deltidial plates.

187

ADELA. ABDAIJ,A HEGAB

188

Genus Rhynchonella Fischer, 1809 Rhynchonella loxiae Fischer, 1809 (Figs. 6) Rhynchonella loxkle Fischer, 1809, p. 35, pl. 1 i fig. 5, 6 Terebratula i,~'tabills Fischer, 1837. p. 147, p i XXlII, fig. 8. Terebratula acuta Fischer, 1843, p. 124, pL IV, figs 7-9 T e r e b r a t u l a loxiae Rouillier, 1 8 4 6 , p . 4 4 1 : Quenstedt, 1868-1871, p. 96, pl. 38, fig. 108. Intemal structure: Median septum long, thick: septalium deep, U shape; septalial plates thick,

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well developed; crura thln, slightly curved have spur shape; dental plates well developed, strongly curved in lower third in late stage of ontogenesis; socket floor very deep; teeth are massive, well developed; outer hinge plates slightly curved. Rfa.jnchonella sp. {Fig. 7) Internal structure: Dental plates well developed; deltidial plates massive and well developed; median septum present, short; teeth extends horizomally into the deep socket floor; crura thick and well developed; outer hinge plates thick and short

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Biostratigraphic zonation of Bathonian-Callovian rocks from Gebel EI-Maghara Northern Sinai, Egypt

CONCLUSIONS The Bathor~lan-Callovian succession oftheGebel EI-Maghara section is rich in brachiopod fossils (Rhynchonellida a n d Terebratulida) which facili-

191

tated the subdivision of the succession into the following seven biozones from top to bottom: Lobo/dothyr/s sp. zone; Ptyctothyrls dorsopllcata zone; Eo__d_esla-Russlrhynchla-Rhactorhonchlazone; Rhy nchone//a masaJ/densts zone; Septa/~/gwr/a sp.-

Fig. 7. Selected sketch transverse serial sections of Rhynchonella sp.

192

ADELA. ABDALLAHEGAB

Ostrea sp. zone; Septaliphoria sobolevi-lvanovieUa a r c u a t a z o n e ; a n d R h a c t o r h y n c h i a oscolicaPraecyclothyrls moeschi donetzlana-Septaliphoria sobo/evt zone. The high degree of d e f o r m a t i o n of m o s t b r a c h i o p o d s p e c i m e n s in the b o t t o m zone (bed No. 11) m a y be d u e to competition in favorable green s h a l e s providing sufficient n o u r i s h m e n t (Makridin, 1964). T h e h i g h d i v e r s i t y of t h e Brachiopod g e n u s Eudesla a c c o m p a n i e d by the bivalvia Eligmus and Gryphaeligmus Lewy c a n be due to relatively c a l m sea w a t e r close to the shore a n d c h a r a c t e r i z e d by occasional high a n d low energy f l u c t u a t i o n s (Feldman, 1982). The prolific food as well a s t h e s u i t a b l e s u b s t r a t e e n c o u r a g e d Ptyctothyrls dorsopllcata S u e s s a n d Rhynchonella masajidensls (in Kehailia Member) to grow to large sizes. C h a n g e s in the n a t u r e of the s u b s t r a t a w a s also reflected on the _frequency of Septallphoria sobo/eviMakridin a n d S.jakovleviMakridin. In the Safa F o r m a t i o n , the g r e e n i s h shale c o n t a i n s the h i g h e s t o c c u r r e n c e , while t h i s f r e q u e n c y dec r e a s e s g r a d u a l l y t o w a r d s the oolitic m a r l y llmestone a n d the h e m a t i t i c yellow shale. The shell size of s p e c i m e n s belonging to Septaliphoria sobolevi Makridin d e c r e a s e s from b o t t o m to top. The envir o n m e n t a l c o n d i t i o n s of t h e Safa F o r m a t i o n are c o n t i n e n t a l at lower part of the s u c c e s s i o n a n d m a r i n e at the u p p e r part. The lower p a r t with a l t e r n a t i n g s h a l e s a n d s a n d s t o n e s w a s deposited u n d e r the regression of sea w a t e r a n d activity of rivers a n d s t r e a m s allowing a c c u m u l a t i o n of fluviatile s e d i m e n t s w h i c h are c h a r a c t e r i z e d by p r i m a r y s t r u c t u r e s on s a n d s t o n e a n d nonfossiliferous shales. The u p p e r p a r t of t h e Safa F o r m a t i o n c o n s t i t u t e s m a r l y limestones, oolitic l i m e s t o n e s a n d m a r l y s h a l e s deposited during a shallow m a r i n e transgressive p h a s e of t h e sea. The shore line of this t r a n s g r e s s i o n is m a r k e d b y coralline limestone with coral heads. The a b u n d a n c e o f b r a c h i o p o d a , mollusca, corals a n d rare e c h i n o d e r m s s u p p o r t s t h e c o n c l u s i o n t h a t the deposition took place u n d e r shallow m a r i n e

conditions. The top o[ t h e Safa F o r m a t i o n is m a r k e d by flinty limestone~ The MasaJ id F o r m a t i o n c o n s t i t u t e s t h i c k shallow m a r i n e s e d i m e n t s (marly limestone, c a l c a r e o u s m u d s t o n e s , m a r l s a n d shales) t h a t were deposited under marine waters The i n t e r n a l s t r u c t u r e of s o m e R h y n c h o n e l l i d fossils have b e e n carried out to elucidate their ontogeny. REFERENCES Abdalla Hegab and H. & Soliman, 1984. Macro and micro structural studies of some Middle Jurassic Eudesiidae from Gebel Maghara, Northern Sinai. Bu/L Fac. Sci, AssOat Univ., 13 (]), 91-I 17. Barthoux, J. C. and DouviUe, H. 1913. Le Jurasaique clans Le Desert a I'Est de I'Isthme de Suez. C. R. Acad. Sct., Paris, CLVII, 265-268. Douville, H, 1916. Les terrains secondalres dana le massif du Moghara, a I'est de I'Isthme de Suez, d'~Ipres les explorations du M. C o y a t Barthoux. Metro Acad. Sct. Parts. Ser. 2, 54, 184 pp~ EI-Far, D. M. 1966. Geology and Coal deposits of Gebel EI-Maghara (Northern Sinai}. Geol. Surv. Paper No. 31. Farag, I. 1957. On the occurrence of Lias in Egypt. Jcx~n. Geol., Sot:. Egypt, 1, No. I, 49-64. Feldman, H. R., Hirsch, F. and Owen, E. F. 1982. A comparison of Jurassic and Devonian Brachiopod Communities: trophic structure, diversity, substrate relations and niche replacement, Th/rd NorthAmr. Paleo. Cony., Proc.. 1, 169-174 Hirsch, F. 1979. Jurassic bivalves and gastropods from Northern Sinai and Southern Israel. Israel Jcxwnal of Earth Sciences, 28(4), 128-163. Makridin, V. P. 1964. Brachiopoda Jorskikh oflogenia Roski platformie nekotorikh prelagachikh k nei oblasti. Nedra Moskva (in Russian). Moon, F. W. and Sadek, H. 1921. Topography and Geology of N. Sinai, Part I, Session 1919-1920. Egypt. Min. Finance, Cairo. Petr. Res. Bull., I0. Said, R. 1962. The geology of Egypt. Elsevier PubL Co. Amst. New York, 377pp. Said, R. and Barakat, M. G. 1958. Jurassic mlcrofosails from Gebel Maghara, Sinai, Egypt. Mk'roImk~r~o~y, 4, 231-272.