New Late Eocene genus Gaziryina (Foraminifera) from theAl Bayda Formation (Shahhat Marl Member),Al Jabal al Akhdar, Northern Cyrenaica, Libya

Ahmed M. Muftah1

and Mohamed Boukhary2

1 Department of Earth Sciences, Faculty of Science, University of Benghazi, P. O. Box 9480, Benghazi, Libyaa_muftah@yahoo.com

2 Department of Geology, Faculty of Science, Ain Shams University, Cairo, Egypt

moboukhary@yahoo.com

ABSTRACT: The foraminifers of the Shahhat Member of the Al Bayda Formation exposed in three sections (at the Wadi Az Zad quarry,and the Wadi Al Kuf and Al Hamamah road cuts) in the region of Jabal Al Akhdar in Libya have been investigated. The rock unit consistsof marly limestone grading into marl in places and is assigned a Late Eocene age according to the presence of forms suggesting the Num-mulites fabianii Biozone, and suggesting also the Early Oligocene age, to which the Shahhat Member has been generally assigned in mostprevious publications should be revised. Nummulites ruetimeyeri de la Harpe 1883 and Chapmanina gassinensis (Silvestri 1904) hasbeen recovered in association with Nummulites fabianii (Prever in Fabiani 1905). Gaziryina pulchellus (Hantken 1883) n. gen. in de laHarpe (1883) has also been retrieved in association with a Nonion-Uvigerina assemblage suggesting relatively deep marine conditions inthe lower intervals of the investigated Late Eocene marly sequence. Nummulites gizehensis (Forskal) is found in the underlying DarnahFormation (Middle Eocene, Lutetian), and the overlying algal limestone of the remaining of the Al Bayda Formation includes speciessuggesting the Nummulites fichteli Biozone of Early Oligocene age.

Key words: Nummulitidae, Upper Eocene, Al Jabal al Akhdar, Northern Cyrenaica, Libya

INTRODUCTION

The Al Bayda Formation was introduced by Röhlich (1974) as asynonym of the Al Kuf Formation of Kleinsmeide and Van DenBerg (1968). This formation was referred by Röhlich (1974) tothe Early Oligocene and it was subdivided into two conform-able members: the lower Shahhat Marl Member and the upperAlgal Limestone Member. El-Mehaghag and Ashahomi (2005)

dated the Shahhat Marl Member as Middle to Late Eocene(NP16-NP20 zones) based on the presence of the calcareousnannofossils Discoaster barbadiensis and D. saipanensis.Moody et al. (2008) correlated the sequence including a highabundance of the distinctive small benthic foraminifers (Nonionspp.) to the Middle - Upper Eocene Cherahil Formation of Tuni-sia. However, the reported presence of Nummulites fabianii

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TEXT-FIGURE 1

Location map for the studied sections at Al Jabal al Akhdar in Northeastern Libya.

(Prever) in the Shahhat Marl Member at Wadi Al Kuf suggests aLate Eocene age for this rock unit. The last mentioned authorsalso reported Eocene calcareous nannofossil assemblages in theexposures of Wadi Al Kuf and Ayn Salloum (Massah) whichalso supports an Eocene rather than an Early Oligocene age.The Shahhat Marl unit was first named by Kleinsmeide and VanDen Berg (1968) as a member of their Al Kuf Formation. Thename was assigned after the historic city of Cyrene “Shahhat”which was founded in 631 B.C. This rock unit represents atransgressive depositional phase intermittently exposed on thenorthern slope of the upper escarpment of Al Jabal Al Akhdar.The unit reaches a maximum thickness of 70m (Röhlich 1974).The overlying Algal Limestone Member yields abundantcoralline red algae with large sized oysters and contains a fewcoral reefs. In other places, the lithology of the sequence gradesto dolomitic limestone. The rock unit is widely distributed inthe region of Al Jabal al Akhdar (Cyrenaica) and has a maxi-mum thickness of 40m (Röhlich 1974). It was deposited underhigh energy, shallow marine (neritic) conditions with a trend toreefal build up on a platform edge (Muftah and Erhoma 2002).This sequence varies laterally and vertically according topaleotopography and sea level fluctuations. The exposure at thetype locality of this rock unit (Al Hamamah roadcut) displays athickness of approximately 15 meters. It is also worth mention-ing that the shallower marly facies of the rock unit exposed atthe “Apollo Fountain” in the historic city of Cyrene includes alevel with intensive burrowing. The intent of this study is to re-vise the age of the Shahhat Marl Member of the Al Bayda For-mation and to analyze the contained Nummulites in the studiedsections of Al Jabal al Akhdar, Libya.

STRATIGRAPHY AND LOCATION

The sampled sections (text-fig. 1) are from three localities: i)Wadi Az Zad quarry (WZQ) situated at the western end of AlJabal Al Akhdar close to Daryanah village, ii) the Wadi al Kufroad cut (WKR) section located at the eastern part of Al JabalAl Akhdar close to Massah village, and iii) the Al Hamamahroad cut section (HR) situated in the eastern part of Al Jabal alAkhdar north of Al Bayda City.

Wadi Az Zad Quarry

The Shahhat rock unit in this locality (text-fig. 2) consists of a12m thick sequence of soft marly limestone with commonnummulitids. Recognized foraminiferal biozones in the rockunit, from bottom to top, are as follows:

The Uvigerina-Nonion Assemblage Biozone: It is defined bythe predominance of the small benthic foraminiferal generaUvigerina and Nonion in association with Gaziryina pulchella(Hantken 1883) n. gen. (Plate 1, Figs. 1-6) and rare planktonicforaminifers. The rocks of this biozone represent the deepest fa-cies of the Shahhat Marl Member and form a lateral equivalentto the same assemblage described by Moody et al. (2008) fromTunisia.

The Nummulites fabianii Biozone: This biozone was introducedby Schaub (1981) in the Mediterranean province and dated asPriabonian. It is also recognized in Oman by Racey (1995).Nummulites fabianii (Prever 1905) (Plate 1, Fig. 10) is impor-tant in defining the Middle-Late Eocene boundary in theTethyan province. The base of the biozone in the Al Bayda For-mation exposed in the Wadi Az Zad quarry is defined by thefirst appearance of N. fabianii in association with Nummulitesruetimeyeri Harpe 1883 (Plate 1, Figs. 12-13) and its top by thefirst appearance of Nummulites fichteli Michelotti, 1841, in as-sociation with Nummulites vascus Joly and Leymerie 1848and coralline red algae.

Wadi Al Kuf road cut

The Shahhat Marl unit in this locality consists of a 12m thick se-quence of marly limestone intercalated with chalky limestoneincluding the Nummulites fabianii Biozone. The underlying se-quence (the Darnah Formation) includes the Nummulitesgizehensis Biozone. It has been deposited under shallower (backbank) conditions as indicated by the presence of frequentmiliolids and Nummulites gizehensis (Forskal 1775) (A-form)and N. bullatus Azzaroli 1952 (Plate 1, Fig. 11) in addition tooysters. An erosional unconformity surface is well exposed atthis locality between the Darnah Formation and the overlyingShahhat Marl Member (text-fig. 3). The Shahhat Marl Member

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Ahmed M. Muftah and Mohamed Boukhary: New Late Eocene genus Gaziryina (Foraminifera) from the Al Bayda Formation, Libya

TEXT-FIGURE 2The view of the Shahhat Marl Member at Wadi Az Zad Quarry.

is overlain by algal limestone of the Al Bayda Formation. TheShahhat Marl Member in the studied section also includes con-cretions, a very thin paleosoil horizon and also frequentbioturbation and few glauconite grains. The Shahhat MarlMember can be subdivided into two foraminiferal biozones,from base to top, as follows:

The Nonion- Uvigerina Assemblage Biozone: This zone is de-fined by a high frequency of the smaller benthic foraminiferalgenera Nonion and Uvigerina together with the larger benthicform Gaziryina pulchellus (Hantken 1883), n. gen.

The Nummulites fabianii Biozone: The biozone in this localityis defined by the presence of Nummulites fabianii (Plate 1, Figs.7-9) in association with N. sp. (Plate 1, Fig. 14). The presenceof Chapmanina gassinensis (Silvestri 1904) is also significantat a higher level within the zone.

Al Hamamah road cut

The Shahhat Marl Member at this locality is composed of a 14mthick sequence of marly limestone containing rare Nummulitesfabianii (Prever in Fabiani 1905) in association with commonGaziryina pulchellus (Hantken in de la Harpe 1883), n. gen. andNummulites cf. N. striatus (Bruguiere 1792). The unit is as-signed to the Late Eocene (Priabonian) Nummulites fabianiiBiozone. The underlying Darnah Formation is a Lutetian num-mulitic limestone included within Nummulites gizehensisBiozone (dominance of A and B forms of the species N.gizehensis (Forskal 1775). The presence of Sphaerogypsinaglobula (Reuss 1848) in this zone is also significant. The se-quence overlying the Shahhat Marl Member (the Algal Lime-stone Member of the Al Bayda Formation) includes theOligocene Nummulites fichteli Biozone (defined according tothe scheme of Schaub 1981). The stratigraphic sections studiedin Wadi Az Zad Quarry, Al Hamamah road cut and Wadi Al Kufroad cut are shown on text-figure 4.

SYSTEMATIC PALEONTOLOGY

The classification of Loeblich and Tappan (1987) and SystemaNaturae 2000 Classification are followed herein for thesuprageneric ranks.

The materials are deposited at University of Benghazi, Facultyof Science, Department of Earth Sciences, Benghazi- Libya.

Kingdom ProtozoaSubkingdom BiciliataInfrakingdom RhizariaSuperphylum RetariaPhylum Foraminifera d’Orbigny 1826Order Rotaliida Delage and Herouard 1896Superfamily Nummulitacea de Blainville 1827Family Nummulitidae de Blainville 1827

Genus Gaziryina Muftah and Boukhary n. gen.

Type species: Nummulites pulchella Hantken in de la Harpe1883.

Etymology of the genus: In memory of Late Abdul-WahidGaziry, Professor of Vertebrate Paleontology, University ofBenghazi, Faculty of Science, Department of Earth Sciences,Benghazi, Libya.

Diagnostic features of the genus: Test is almost perfectly flat,with a pronounced coarse trabecule comprising a boss or bun-dles of granules centrally planispiral involute, without alar pro-longation, and with transverse trabecules. As the Spiral growswith added whorls, then chambers become higher rather thanlonger. The ntogeny reflects tight to looser coiling.

Discussion: The taxon was originally assigned to the genusNummulites Lamarck 1801. However, a new genus is erectedbased on the presence of transverse trabecules, the absence ofthe characteristic marginal cord, and the lack of alar prolonga-tions, which are important characters for the definition of thegenus Nummulites s. str.

Range: The species is strictly of Late Eocene (Priabonian)stratigraphical range.

Gaziryina pulchellus (Hantken 1883), n. gen. (in de la Harpe 1883)Plate 1, figs. 1-6

Nummulites pulchella Hantken in DE LA HARPE 1883, p. 160, pl. 5,figs. 15–21.

Nummulites pulchellus Hantken. – BOMBITA and MOISESCU 1968,pl. 3, figs. 5–8. – HERB and HEKEL 1975, p. 126–127, text-figs.26–31, pl. 2, figs. 4–13.

Description: Megalospheric (A-dimorphic form): Only themegalospheric forms are recorded in the studied sections. Testthin, flat, with pronounced large trabecules comprising a boss orbundles centrally, septal filaments radial near the center, slightlycurved externally; trabecules are clear. Diameter ranges from2.3 to 3.9mm; thickness ranges from 0.42 to 0.75mm.

Equatorial section: Spire regular, chambers higher than long, asthe ontogeny is from tight to lax with no alar prolongation in ax-ial sections. The number of whorls versus radius is as follows:two whorls in a radius of 1.97mm, three whorls in 2.0mm.Protoconch size ranges from 0.08 to 0.15mm (Fig. 5).

Material: Thirty-two specimens collected from the three stud-ied sections of Al Jabal al Akhdar, Northern Cyrenaica, Libya.

Comparison: Nummulites aff. N. pulchellus Hantken as de-scribed by Morsi et al. (2003) from Na’alun, Egypt, is possibly

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TEXT-FIGURE 3Disconformity surface between the nummulitic Darnah Formation andthe overlying Shahhat Marl Member at the Wadi al Kuf road cut section.

the ancestral form of Gaziryina pulchellus (Hantken 1883), n.gen. because both the diameter of the test and the protoconchdiameter in the former species are smaller and the coiling istighter and this lineage undergoes tight to looser coiling throughontogeny.

CONCLUSION

The Shahhat Marl Member of the Al Bayda Formation in WadiAz Zad, Al Hamamah and Wadi al Kuf sections have been in-vestigated micropaleontologically on the basis of larger benthicforaminifers.

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TEXT-FIGURE 4Stratigraphic sections studied in Wadi Az Zad Quarry, Al Hamamah road cut and Wadi al Kuf road cut.

PLATE 1

1,2 Gaziyrina pulchellus (Hantken 1883) n. gen., sideviews, Wadi Az Zad Quarry, bed (1), sample (1).

3-5 Gaziyrina pulchellus (Hantken 1883) n. gen., axialsections, Wadi Az Zad Quarry, bed (1), sample (1).

6 Gaziyrina pulchellus (Hantken 1883) n. gen., equato-rial section, Wadi Az Zad Quarry, bed (1), sample (1).

7 Nummulites fabianii, (Prever 1905), side view, WadiAl Kuf road cut, bed (3), sample (E8).

8 Nummulites fabianii, (Prever 1905), side view, WadiAl Kuf road cut, bed (3), sample (E7).

9 Nummulites fabianii, (Prever ), side view, Wadi AlKuf road cut, bed (3), sample (E8).

10 Nummulites fabianii, (Prever ), equatorial section,Wadi Az Zad Quarry, bed (4), sample (5).

11 Nummulites bullatus, Azzaroli 1952, side view, WadiAl Kuf road cut, bed (1), sample (E1).

12,13 Nummulites ruetimiyeri Harpe 1883, side view andequatorial section respectively, Wadi Az Zad Quarry,bed (4), sample (5).

14 Nummulites sp., equatorial section, Wadi Al Kuf roadcut, bed (3), sample (E8).

micropaleontology, vol. 59, nos. 2–3, 2013 107

Ahmed M. Muftah and Mohamed Boukhary Plate 1

A Late Eocene (Priabonian) age has been assigned to the stud-ied rock unit based on the age of the established Nummulitesfabianii Biozone. Gaziryina n. gen. has been described herein.

ACKNOWLEDGMENTS

We would like to thank Mr. Ibrahim El-Mahdi of the ArabianGulf Oil Company in Ganfouda and Mr. M. Al-Jaroushi ofBenghazi University for their assistance in samples preparation.The authors wish to thank Prof. Omar Cherif, of the EgyptianNational Authority for Remote Sensing and Space Sciences(NARSS). Drs Galina P. Nestell and Merlynd K. Nestell, De-partment of Earth and Environmental Sciences, University ofTexas at Arlington, USA, for reviewing the manuscript. Ourgratitude also is extended to Mr. Ahmed Abdulnassar of AssiutUniversity for his assistance in the SEM photography.

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TEXT-FIGURE 5Spiral diagram shows the relation between the number of whorls andcorresponding radius in Gaziryina pulchellus (Hantken 1883) n. gen.

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