Biostratigraphy of the Late Paleozoic succession in ...

N. Jb. Geo!. Palaont. Mh.

Stuttgart,

Mai 1989

Biostratigraphy of the Late Paleozoic succession in Gabal Ekma, southwestern Sinai, Egypt By Mahmoud Kora, Mansoura With 6 figures in the text KORA, M. (1989): Biostratigraphy of the Late Paleozoic succession in Gabal Ekma, southwestern Sinai, Egypt. - N. Jb. Geo!. Palaont. Mh., 1989 (5): 293-307; Stuttgart. Abstract: Two biostratigraphic units are described from the Carboniferous succession belonging to the Abu Durba Formation; a lower Glomospira-Nodosinella Assemblage Zone and an upper Idiognathodus-Neognathodus Assemblage Zone, with a barren interzone. Nine species of brachiopods, bryozoans, conodonts and foraminifers were not previously recognized in the Carboniferous of Egypt. These assemblages suggest an age equivalent to the Moscovian or Middle Pennsylvanian. Correlations based on the assumption that the shales of the Abu Durba Formation are the lateral equivalent of the Lower Carboniferous carbonates of the Urn Bogma Formation are not supported. Zusammenfassung: Aus der zur Abu-Durba-Formation gehorenden Karbon-Abfolge im siidwestlichen Sinai werden zwei biostratigraphische Einheiten beschrieben: eine untere Glomospira-Nodosinella Vergesellschaftungs-Zone und eine obere Idiognathodus-Neognathodus Vergesellschaftungs-Zone. Die beiden Zonen werden durch einen fossilleeren Bereich getrennt. Yon den vierzig Arten (Brachiopoden, Bryozoen, Conodonten und Foraminiferen) waren neun bis jetzt nicht aus dem agyptischen Karbon bekannt. Die Faunen-Vergesellschaftungen der Abu-Durba-Formation zeigen ein jiingeres Karbon-Alter (Moskovien oder mittleres Pennsylvanien) an. Deshalb konnen Vermutungen, daB die Tonsteine der Abu Durba Formation ein laterales A.quivalent der Urn Bogma Formation waren, nicht bestatigt werden.

Introduction In northern Egypt, stratified Paleozoic outcrops are known from the western side of the Gulf of Suez and from Sinai. In southwestern Sinai, the Precambrian basement is covered mainly by shallow marine and continental sandstones intercalated with few dolostones and shales of Paleozoic age. These rocks are particularly well exposed in two disconnected areas; the Urn Bogma area to the east of Abu Zenima and in Gabal Ekma to the south of Wadi Feiran, in the vicinity of Abu Durba. Opinions differ how to correlate the Paleozoic rocks in/and on both sides of the Gulf of Suez. This is attributed not only to the poorly fossiliferous nature of most of these rocks but also to their discontinuous exposure in the regIon.

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In the present study, the distribution of both macro- and microfauna in the Carboniferous succession belonging to the Abu Durba Formation in southwestern Sinai is discussed. The identified faunal assemblages are compared with other Carboniferous fossils known from the Gulf of Suez region to delineate the stratigraphic position of the Abu Durba Formation. The importance of these fossils as a clue to the environmental conditions that prevailed during the deposition of that succession is also considered. The extension of the Paleozoic rocks was followed in the field and illustrated on a modified part of the geological map of Sinai (EYALet al. 1980). Two sections were sampled in detail in the studied area (Fig. 1). The first extends through the

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Late Paleozoic succession in Gabal Ekma

295

southern slopes of Gabal Ekma, immediately to the east of EI Belayim Bay. The other section was measured in the northern cliffs of that mountain near the entrance of Wadi Feiran. All the studied materials are deposited in the Geology Department, Faculty of Science, Mansoura University, Mansoura, Egypt. Research history The Paleozoic rocks of Gabal Ekma were first studied by HASSAN(1967) who distinguished a 122 m thick unit of sandstones and fossiliferous shales of proposed Upper Carboniferous age, exposed to the east of EI Belayim Bay. This unit overlies a 510 m thick sandstone succession of Early Paleozoic, mostly CambroOrdovician age. A limestone bed containing stromatolites and small archaeocyathids indicating an Early Cambrian age was discovered by OMARA(1972) underlying this huge sandstone interval. SAID (1971) gave the name "Durba Formation" to the fossiliferous shalesandstone unit described by HASSAN(1967) in the area and considered it to be of Early Carboniferous age (Fig. 2). This fossiliferous unit was further subdivided into a lower unit "Abu Durba Formation" and an upper unit "Aheimer Formation" of Early and Late Carboniferous ages, respectively (ISSAWIet al. 1981 and ISSAWI&Jux 1982). However, the whole Late Paleozoic sequence exposed in the area was assigned to the so called Nubia "B" of the Gulf of Suez petroleum geologists (BUNTER 1984), of Permo-Carboniferous age. Recently, the name Abu Durba Formation was again used for this facies in the Abu Durba area by BELEITYet al. (1986) who considered the formation to be of Early Carboniferous

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correlation chart of the Carboniferous

rock units used in the Sinai.

296

Mahmoud Kora

age, underlying Early Cretaceous and overlying Early Paleozoic clastics. Similarly, KLITZSCH&WYCISK(1987) supposed the Durba Shale together with the underlying Naqus Formatin and an overlying unit "Ataqa Formation" to be of Early Carboniferous age (Fig. 2). The Carboniferous macro- and microfauna of Urn Bogma area were revised by KORA &Jux (1986) and KORA (1986). Also, the classical Late Paleozoic fauna of the western side of the Gulf of Suez (WALTHER1890) were recently reviewed by ABDALLAH KENA WY (1966),

& EL ADINDANI

(1965),

SAID & EISSA (1969),

OMARA

& VANGEROW

ABDEL RAHMAN

(1985)

(1965),

OMARA

and HERBIG

&

& Kuss

(1988). The Carboniferous

faunas of Gabal Ekma

Generally, the fossils found are neither in great abundance nor in a good state of preservation. The collected macrofaunas are mainly brachiopods and bryozoans in addition to rare molluscans and ossicles of echinoderms. The recovered microfossils are mostly arenaceous foraminifers and conodonts. Brachiopods The specimens encountered are mainly spiriferids and strophomenids. The seven species identified (Fig. 3a-i) are associated with moderately large spiriferids comparable to Frechella LEGRAND-BLAINrecently described from the Upper Serpukhovian of the Algerian Sahara (LEGRAND-BLAIN1986). Similarly, the identified species of Antiquatonia (Fig. 3i) bears striking similarity to some semireticulate productoids described from the Westphalian of Morocco (TERMIER& TERMIER1950: 178). No specimens with ornament typical of Neospirifer fasciger

Fig. 3. Brachiopods

and bryozoans from the Abu Durba Formation. stated, all specimens are normal size.

Unless otherwise

a-c: Neospirifer cameratus (MORTON); a, b: ventral views; c1,2: posterior views. d: Choristitella podolskensis (IvANOV); ventral view. e: Choristites d. mosquensis BUCKMAN;dorsal view. f: Hustedia sp.; £1,2: dorsal and ventral views. g: Streptorhynchus crenistria PHILLIPS;ventral view. h: Chonetinella sp.; hl,2: ventral valve viewed dorsally and ventrally. i: Antiquatonia sp.; dorsal view. J: Rhombotrypella astragaloides NIKIF. jl: general shape of zoarium, x 0.6; j2: tangential section, x 9; j3: longitudinal section, x 9. k: Fistulipora sp. kl: general shape of zoarium, x 0.6; k2: longitudinal section, x 9; k3: transverse section, x 9. I: Polypora sp., x 0.9. m: Fenestralia d. sanctiludovoci PROUT, x 1.2. n: Fenestella d. carinata M'Coy. 0: Fenestella aff. compressa ULRICH, x 0.8.

Late Paleo'ZOICsuccession in Gabal Ekma

297

298

Mahmoud Kora

(KEYSERLING)reported to occur in the area by ISSAWIet al. (1981) were encountered in the studied succession. Streptorhynchus crenistria PHILLIPS(Fig. 3g) was already described from the Carboniferous of Wadi Araba in the Eastern Desert (WALTHER

1890).

Bryozoans Exceptionally, well preserved fragments are encountered (Fig. 3;-0). The six species identified are dominated by the fenestellids; stenoporids seem to be restricted to Rhombotrypella astragaloides NIKIF (Fig. 3;). Cyclostomates represented by Fistulipora sp. (Fig. 3k) were also recorded from Wadi Araba in the Eastern Desert (WALTHER1890). Some of the collected fenestellids (Fig. 3m-o) are tentatively assigned to very similar species described by DUNCAN (1969) from the Redwall Limestone of North Arizona. Similarly, ISSAWII!cJux (1982) reported the presence of Polypora sp. (Fig. 31) from the Abu Durba area. Conodonts Five species can only be positively identified from the studied material (Fig. 4a-d). The remaining fragmentary forms (e.g. Fig. 4e) deserve further study. Idiognathodus delicatus GUNNELL (Fig. 4b) and Neognathodus medexultimus MERRILL(Fig. 4c) are the most conspicuous elements encountered. Forms

Fig. 4. Conodonts

and foraminifers from the Abu Durba Formation. Unless otherwise stated, all specimens are X 60. a: Idioprioniodus conjunctus (GUNNELL); outer side view of MI element, x 30. b: fdiognathodus delicatus GUNNELL; bl-3: upper, lower and side views of Pa element, x 44. c: Neognathodus medexultimus MERRILL; d,2: upper and side views of Pa element. d: Hindeodus minutus (ELLISON); dl,2: inner-lateral views of N element; d3: side view of Pa element. e: Conodonta indet. f: Hyperammina rugosa WATERS, X 30. g: Hyperammina compressa PAALZOW, X 30. h: Nodosinella aegyptiaca SAID & EISSA. i: Ammodiscus annularis (BRADY). i: Ammodiscus roessleri (SCHMID). k: Ammodiscus nitidus PARR. I: Ammodiscus semiconstrictus WATERS var. regularis WATERS. m: Ammodiscus grandis HOLLAND. n: Agathamminoides gracilis VANGEROW. 0: Glomospira diversa CUSHMAN & WATERS. p: Glomospira simplex HARLTON. q: Orthovertella protea CUSHMAN & WATERS. r: Orthovertella sp. s: Tolypammina aheimerensis SAID & EISSA.

t: Ammovertella

delicata REITLINGER.

Late Paleozoic succession in Gabal Ekma

299

300

Mahmoud Kora

similar to Jdiognathodus excelsus (STAUFFER &:PLUMMER) were already recorded from the western side of the Gulf of Suez (OMARA &:KENA WY 1966, SAID &:EISSA 1969). The distinction between Streptognathodus and Idiognathodus on the basis of the presence or absence of a median trough (AUSTIN &:RHODES 1981) is not followed here. SAVAGE &:BARKELEY (1985) considered this difference to be diagnostic within this group only at the species level.

Foraminifers The identified 25 species are almost exclusively arenaceous and agglutinating (Fig. 4f-t). Calcareous forms are rare and restricted to the calcareous shale horizon near the top of the formation. Individuals belonging to the families Ammodiscidae, Nodosinellidae and Astrorhizidae outnumber those of the families Saccamminidae, Lituolidae and Paleotextularidae. As regards specific levels, Ammodiscus followed by Hyperammina and Tolypammina are more diversified than all other genera (Fig. 4f-t). Many of these foraminifers were recorded from the western side ofthe Gulf of Suez (OMARA&:KENAWY1966, SAID&:EISSA1969 and ABDEL RAHMAN 1985). The species Glomospira diversa CUSHMAN &:WATERS, Lituotuba regularis REITLINGERand Bathysiphon curvus MOREMANwere also recorded from the study area by ISSAWIet al. (1981). The Carboniferous faunas identified from Gabal Ekma fills a list of more than 40 species. Indeed, most of them were already described by different workers from the Gulf of Suez region. Yet nine species were not previously recognized in the Carboniferous of Egypt. Thus, two brachiopods: N eospirifer cameratus (MORTON) and Choristitella podolskensis (IVANOV),one bryozoan: Rhombotrypella astragaloides NIKIF, four conodonts: Idioprioniodus conjuctus (GuNNELL), Idiognathodus delicatus GUNNELL, Neognathodus medexultimus MERRILL and Hindeodus minutus (ELLISON) in addition to two foraminifers: Septammina bradyi CUSHMANand Ammovertella delicata REITLINGERare identified for the first time in the Carboniferous of the Sinai (Figs. 3 and 4).

Biostratigraphy

and age

The stratigraphic distribution of the fossils encountered in the two measured sections is illustrated in Figs. 5 and 6. It is observed that while foraminifers are recovered from many black shale horizons in the lower and the upper parts of the succession, conodonts and brachiopods as well as the bryozoans are restricted only to the upper part of the formation. Laterally, the foraminifers become more diversified in the southern part of the study area. Meanwhile, brachiopods and bryozoans ar better preserved northwards. Based on the stratigraphic distribution of the identified fossils, two local biozones are recognized in the Abu Durba

Formation;

a lower Glomospira

and an upper Idiognathodus-Neognathodus

- Nodosinella

Assemblage

Zone

Assemblage Zone, with a 50 m thick J

Late Paleozoic succession in Gabal Ekma

301

barren interzone (Figs. 5 and 6). The following comments summarize the characteristics of these biostratigraphic units. Glomospira - Nodosinella Assemblage Zone This biozone is characterized by an association of arenaceous foraminifers dominated by Glomospira diversa CUSHMAN& WATERSand Nodosinella aegyptiaca SAID&EISSA.Foraminifers which are common in this zone include Ammodiscus semiconstrictus WATERSvar. regularis WATERS,A. annularis (BRADY),A. roessleri (SCHMID),A. grandis HOLLAND, Hyperammina rugosa WATERS,H. compressa PAALZOW,Glomospira simplex HARTLON and Agathamminoides gracilis VANGEROW,in addition to many less frequent forms (Fig. 5). These taxa are recorded concurrently in the lower 52 meters of the Abu Durba Formation comprising the basal dark grey shales and siltstones that overlie the Naqus Formation in the southern section. The zone is recorded from a 55 m thick sandstonesiltstone-shale sequence in the northern section which is comparatively poorer in its fossil yield (Fig. 6). Although the encountered foraminifers are long-ranging throughout the Late Paleozoic, yet the above mentioned species which are common to abundant in southwestern Sinai are characteristic Pennsylvanian forms. Glomospira diversa CUSHMAN& WATERS,G. simplex HARLTON, Hyperammina rugosa WATERSand Ammodiscus semiconstrictus WATERSwere described from the Pennsylvanian of Texas (CUSHMAN & WATERS 1928). The encountered Ammodiscus roessleri (SCHMID)is very similar to those from the Westphalian of the Ruhrgebiet in West Germany (VANGEROW1964). This species and also the Agathamminoides gracilis VANGEROWare common to bundant constituents in the Westphalian foraminiferal assemblage described by OMARA&VANGEROW(1965) from the Abu Darag in the western side of the Gulf of Suez. Similarly, Nodosinella aegyptiaca SAID & EISSAand Tolypammina aheimerensis SAID & EISSAwere first described from the Aheimer and the Abu Darag Formations which are considered to be of Upper Pennsylvanian age (SAID & EISSA1969). It seems feasible therefore to consider a Pennsylvanian age for the present Glomospira-Nodosinella assemblage. Further substantiation is provided from the age of the upper biozone. Idiognathodus

- Neognathodus

Assemblage Zone

This conodont zone is distinguished by the presence of ldiognathodus delicatus GUNNELL and Neognathodus medexultimus MERRILLin the upper part of the studied succession. Other conodonts which occur in the zone include ldioprioniodus

conjunctus

(GUNNELL),

ldiognathodus

excelsus

(STAUFFER

& PLUMMER)

and

Hindeodus minutus (ELLISON).These elements are identified from a 12 m black shale horizon overlying a hard dolostone bed and underlying a reddish brown sandstone bed near the top of the Abu Durba Formation. This interval is charac-

302

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