Stratigraphy and Microfacies Analyses of The Al Faidiyah and Benghazi Formations at Al Fatiah, Al Huarry and Al Abyar Quarries, NE Libya

Three quarries named Al Fatiah Cement, Al Huarry Cement and Al Abyar are located to the northeastern part of Libya consists of carbonate rocks of Miocene age. The main objectives of this study based on microfacies analyses are construct the depositional environment with comprehensive stratigraphical correlation of the study areas. The Al Fatiah Quarry has been divided into three microfacies which are operculinid packstone microfacies, algal packstone microfacies and moluskan packstone grading to grainstone microfacies, one species of large benthic foraminifera is found to be abundant (Operculina complanata). Accordingly, the Al Faidiyah Formation was deposited in a continental shelf (outer to middle neritic zones) environment. Al Huarry Cement Quarry has been divided into five microfacies which are algal boundstone microfacies, amphisteginid - algae packstone microfacies, amphisteginid grainstone microfacies, algal - bryozan packstone microfacies and amphisteginiid - bryozoan - algal boundstone microfacies, one species of large benthic foraminifera is found to be abundant and well preserved (Amphestegina cf. lessonii). Accordingly, the Benghazi Formation was deposited in an inner self to open marine shelf environment. On the other hand, the Al Abyar Quarry has been divided into two microfacies which are pelloidal packstone microfacies and miliolid wackestone–packstone microfacies, suggesting that the sedimentation was of low energy under very shallow marine to restricted environment.


Introduction
Al Jabal Al Khdar is a highland area which encompasses the northern most part of Cyrenaica north east Libya, it is consists of Upper Cretaceous to Tertiary marine deposits, but Jurassic and Lower Cretaceous marine deposits are known from the exploratory oil wells.The Al Jabal Al Khdar is more than 200 km long and 75 km wide.Al Faidiyah and Benghazi formations represent a portion of Al Jabal Al Akhdar region.The Al Faidiyah Formation was introduced by Pietersz (1968) it ranges in age (Aquitanian-Burdigalian) and Benghazi was introduced by Gregory (1911) it ranges in age (Langhian-serravalian ) these two formations were deposits in shallow marine environments (Klen,1974).

Objective
The purpose of this study to discuss the microfacies analyses in order to construct the depositional environment with comprehensive stratigraphical correlation of the study quarries.

Methodology
About 20 surface samples were collected at a maximum interval 10 m from three quarries and were subjected to thin sections to determine the differential sedimentological and diagenetical features an according to Dunham classification (1962).The analysis was done in laboratory at Arabian Gulf Oil Company.

Al Fatiah Cement Quarry (Al Faidiyah Formation)-lower Miocene (Middle Aquitanian)
Al Fatiah Cement Quarry is represented by 35 m thick sequence of Al Faidiyah Formation.The name was introduced by Pietersz (1968) from the village of Al Faidiyah about 16 km southeast of Shahhat (Cyrene) city.Al Faidiyah Formation received several paleontological works such as El Safori and Muftah (2007) and Muftah (2014).
The stratigraphic sequence of the Al Fatiah Cement Quarry has been examined in three traverses (as shown in Figure 2).These traverses have been divided into-three microfacies which are operculinid packstone microfacies, algal packstone microfacies and molluskan packstone grading to grainstone microfacies and correlated in them in traverses have been difficult.
The Al Faidiyah Formation in the study area is characterized by grain supported fabric (packstone texture), white to off white colored, moderately hard, medium to coarse grains, thickly bedded with local moderately fractured due to tectonic events and may industrial activities, with some micritic matrix, rare gypsum and calcite cements, rarely glauconitic, with some bioclasts which are represented by Operculina, worm tubes, bryozoan, pelecypods, gastropods, algae, echinoids, and undifferentiated shell fragments.

Traverse I:
Two microfacies have been established at this traverse from bottom to top:

Operculinid packstone microfacies:
It characterized by white colored, fine grained, soft to moderately hard, thickly bed with local highly fractured, some micritic matrix, rare gypsum and calcite cements, rare glauconite grains.The bioclasts are represented by presence of the benthonic foraminifera Operculina complanata, with serpulid worm tubes, rare algae peloids, molluskan (mainly Oysters and some gastropods) fragments (Figure 3a) and a few echinoides embedded within the micritic matrix.Porosity is of intercrystalline type and the thickness reaches up to 5.5 m.

Molluskan packstone grading to grainstone microfacies:
It characterized by milky to white coloured, medium grained, moderately hard, thickly bedded with local fractured and slightly krastified, micritic matrix.The bioclasts are represented by common recrystallized mollusks, Serpulid worm tubes, bryozoan debris and some shell fragments within micritic matrix.This microfacies shows diagenesis process mainly on fossils due to dissolution effect (Figure 3b).The porosity is of moldic to shelter types and the thickness reaches up to 4.5 m .

Traverse II:
Two microfacies have been established at this traverse from bottom to top:

Algal packstone microfacies:
It characterized by white to light grey colored, fine grained, medium hard, thickly bedded with local fractured and poorly karstified, isopacheous cement rimmed algal grains, glauconitic in part.The bioclasts are represented by presence fragments of coralline red algae etching by dolomite crystals and filling pore spaces, few echinoids and pelecypods (Figure 3c).The porosity is of interskeletal type and the thickness reaches up to 3.5 m.Shaltami et al., 2018 Faculty of Marine Resources, Alasmarya Islamic University, Libya.

Molluskan packstone-gainstone microfaceous:
It characterized by white to yellowish colored, medium to coarse grained, medium hard, thinly bedded with local fractured and karstified, micritic matrix in part, rare dolomite and gypsum crystals, (Figure 3d) isopacheous calcite cement.The bioclast is represented by mainly mollusks (Oysters) fragments.Porosity is of interskeletal-intercrystalline type and the thickness reaches to 6.5 m.

Travers III:
One microfacie has been established at this traverse:

Molluskan packstone with local grading to grainstone microfacies:
It characterized by white to off white colored, fine to medium grained, soft to medium hard, thickly bedded with local fractured, common micritic matrix, common calcite and a few dolomite cements.Bioclasts are represented by common partially recrystallized mollusks (oysters), gastropoda, serpulid worm tubes and echinoides with rare undifferentiated fossils fragments.Common replacement of calcite to oyster shells (Figure 3f).Porosity is poorly intercrystalline type and the thickness reaches up to 10 m.

Age of Al Faidiyah Formation
The Al Faidiyah Formation dated as Late Oligocene-Early Miocene by Rohlich (1974) and El Mehdawi and El Beialy (2008).However, Early Miocene age is according to El Hawat and Shelmani (1993)

E-31
ISSN: 2413-5267 The Benghazi Formation in the study area is characterized by grain supported fabric (packstone to boundstone textures), white to grey colored, moderately hard, medium to coarse grains, thickly bedded with local highly fractured due to tectonic events and may industrial activities) and karstified filling by celestite, with some micritic matrix, and calcite cement, rare gypsum and glauconite grains, with some bioclasts which are represented by common algae, Operculina, worm tubes, bryozoan and rare pelecypods, gastropods, echinoids, and undifferentiated shell fragments embedded within micritic matrix.

Traverse I:
Two microfacies have been established at this traverse from bottom to top:

Algae boundstone microfacies:
It characterized by white colored, medium to hard, thinly bedded with highly local fractured.The bioclasts represented by coralline red algae with rare Amphistegina sp.operculinid fragments and molluskan (pelecypoda-gastropoda) fragments (Figure 6a).Porosity is of intraskeletal type and the thickness reaches up to 2 m.

Algae-amphisteginid packstone microfacies:
It characterized by white to light grey in part colored, medium to coarse grained, thickly bedded with highly fractured, karstified and solution cavities filled by celestite, dolomite and calcite crystals, glauconitic in part.The bioclasts represented by common benthonic foraminifera Operculina sp., Amphistegina sp., algal pelloids and a few fossils debris embedded within micritic matrix (Figure 6b).Porosity is of interskeletal type and the thickness reaches upto 8 m.

Traverse II:
Three microfacies have been established at this traverse from bottom to top:

Algal-amphisteginid grainstone microfacies:
It characterized by milky to white colored, occasionally gray in part.Thinly bedded and highly fractured in part with and highly solution filled by celestite.Common dolomite euhedral crystals, with rare in gypsum.The bioclasts represented by common reworked red algae (Figure 6c), rare Amphistegina and Operculina fragments in parts.Porosity is of intercrystalline type and thickness reaches upto 1.5 m.

Algal-amphisteginid packstone microfacies:
It characterized by white to light grey in part colored, fine to medium grained, softmedium hard, thickly bedded which with local fractured, macritic matrix with dolomite and calcite crystals.The bioclasts represented by common Amphistegina sp. and algal debris with rare in echinoid fragments (Figure 6d).Porosity is of interskeletal type and the thickness reaches upto 5 m.

Algal-bryozan packstone microfacies:
It characterized by white to light gray in part, medium grained, soft-medium hard, thickly bedded which with local fractured and karstified filled by celestite.Macritic matrix with dolomite and calcite crystals.The bioclasts represented by common coralline red algae and bryozoan and few scleractinian corals.It shows diagenesis process mainly on fossils due to dissolution effect (Figure 6e).Porosity is of vuggy-interskeletal types.Thickness reaches up to 3.5 m.

Travers III:
Two microfacies have been established at this traverse from bottom to top:

Algae-amphisteginid packstone microfacies:
It characterized by white to smoky colored, medium grained, hard thickly bedded with local fractured and highly krastified filled by stalactite, micrtic matrix, dolomite, calcite and rare gypsum crystals.The bioclasts represented by common coralline red algae, with few echinoid and shell fragments which are embedded within micritic matrix (Figure 6f).Porosity is intercrysalline and micro vuggy types and the thickness reaches upto 3 m.

Amphsiteginid-bryozoan-algal boundstone microfacies:
It characterized by white to milky colored, hard, thickly bedded with local fractured and poorly krastified filled by celestite, micrtic matrix, glauconite grains.The bioclasts represented by common coralline red algae, Amphistegina sp.algal pelloids and some fossil fragments serpulid worm tubes and bryozoa, encrustation of bryozoa with red algae is also common phenomena at this microfacies which is indicating a slow rate of sedimentation (Figure 6g).

Stratigraphic Correlation
During field work the stratigraphic correlation were made in Al Huarry Cement Quarry (Figure 7) this correlation obtained by measure tow traverses T1, T2 and T3 is unexposed of the bottom and difficult to tie this tram with own correlation (it is doubtful).The datum is lower part of algae-amphisteginid packstone microfacies, the correlation between them was constructed in order to indentify lateral or vertical lithological changing along the study area.
The traverses being correlated are approximately along 600 km from NE-SW.This correlation indicates the following observations: A. Benghazi Formation is recorded in all studied sections with maximum thickness of (about 35 m as recorded in the Al Huarry Cement Quarry and generally shows gradual thickness increased toward SW direction.B. The established microfacies have been correlated, considering the base of algaeamphisteginid packstone microfacies as datum of this correlation.This microfacies is increased towards T1 at SW. On the other hand, algae-amphisteginid packstone microfacies is underlain by algal boundstone microfacies at T1 traverse which is laterally changed to algal-amphisteginid graistone microfacies at T2.The amphestegined contained microfacies are suggested to be deposited under shallow platform of for reef setting.

Age of Benghazi Formation
The stratigraphic position and fossil assemblage suggest that the Benghazi Formation was deposited during Middle Miocene (Rohlich, 1974), Shaltami et al. (2018b) found that the ages derived from strontium isotope analysis of crystalline calcites are gave an age Late Burdigalian-Early Serravallian (13.24-17.45Ma) for the Benghazi Formation.

Traverse I:
Two microfacies have been established at this traverse from bottom to top:

Pelloidal packstone microfacies:
This microfacies exhibits grain supported fabric (dolostone packstone texture).Which is characterized by gray to dark gray, smoky in part, medium to coarse crystalline,thickly bedded with high fractured and krastified, micritic matrix with dolomite crystal, The bioclasts represented by common pelloids, ostracoda, Amphistegina sp.(Figure 9a), and undifferentiated miliolids, pelacypoda including Pecten, and gastropoda fragments.The porosity is of intercrystalline locally becomes becoming vuggy type, and the thickness reaches upto 4 m.

: Miliolid wackestone microfacies
This microfacies exhibits mud-grain supported fabric (wackestone texture); which is characterized by light gray to gray and occasionally dark gray in part, medium crystalline grained, very hard, massive bed with high fractured, micritic matrix with dolomite crystals, The bioclasts are represented by common miliolids (Quinqueloculina spp., Borelis melo, Triloculina spp., Spirolina sp., and few molluskan, ostracoda and pelloids (Figure 9b).Porosity is of interskeletal type becoming vuggy in parts and the thickness reaches upto 4 m.Al Faidiyah Formation in Al Jabal Al Akhdar represents a series of coarsening-up cycles that suggest sedimentation in high-energy sand shoal bar and channel (El Hawat and Shelmani, 1993).However, Rohlich (1974) suggests that the depositional environment was in shelf environment with local brackish element based on the paleontological contents and the lithological type of the formation.In the study area, this formation contains organisms of shallow marine as commonly represented by coralline red algae and Operculina complanata with some mollusks, echinoids, pelloids, bryozoans and other benthonic foraminifers, according to these the Al Faidiyah Formation was deposited in continental shelf (outer to middle neritic) with local brackish affinity (Figure 10).

Depositional Environment of Benghazi Formation at Al Huarry Quarry
The depositional environment of Benghazi Formation was previously studied by several authors.Abdulsamad and Bu-Argoub (2006) suggested this Formation was deposited on an open shallow marine shelf environment.In the study area, this Formation contains shallow marine organisms however the lower part represented by common algae microfacies and amphistigind microfacies with red algae, echinoids, bryozoans, mollusks and benthic foraminifera while the upper part is composed of boundstone alternating with grainstone where, debris of echinoids, bryozoans and mollusks are common, accordingly the Benghazi Formation was deposited under an inner self to open marine shelf environment (Figure 10).

Depositional Environment of Benghazi Formation at Al Abyar Quarry
Pelloids are generally formed in shallow marine low energy platform carbonate setting such as in the lagoon area of Bahama bank (Prothero and Schwab, 2004).Benthonic foraminifers (for example miliolids) suggest restricted low energy depositional environment; Prothero and Schwab (2004) indicated that Benghazi Formation represents an open shelf grading upwards to restricted platform and restricted lagoon-salina condition of Wadi al Qattarah Formation at Soluq area.In the study area, the Benghazi Formation at Al Abyar quarry contains organisms of restricted shallow marine as in the algae-pelloidal microfacies and miliolids microfacies where, few mollusks, ostracods and pelloids are present.Accordingly, the Benghazi Formation at the study area is deposited under lagoonal environment (Figure 10).

Conclusion
Three microfacies at Al Fatiah Quarry which are operculinid packstone microfacies, algal packstone microfacies and molluskan packstone grading to grainstone microfacies have been recognized at this section.The suggested depositional environment of Al Faidiyah Formation is continental self of outer to middle neritic environment.
Two microfacies at Al Abyar Quarry, pelloidal packstone microfacies and miliolid wackestonepackstone microfacies have been recognized at this locality.The suggested depositional environment of Benghazi Formation is under an inner shelf environment.

Figure ( 1
Figure(1)  shows that the first section is located at Al Fatiah Cement Quarry between latitude 32°35'46ʺ N and longitude 22°43'21ʺ E (about 25 km east of Dernah city).The second section is located at Al Huarry Cement Quarry (about 18 km south west of Benghazi city).This section is represented by limestone and terra rossa soil between latitude 75°31'59ʺ N and longitude 73°32'00ʺ E. The third section is located at Al Abyar Quarry between latitude 32°37ʹ60ʺ N and longitude 20°36ʹ98ʺ E (of about 60 km east of Benghazi city).This section is represented only by limestone.

Figure 1 .
Figure 1.Location map of the study area.
Stratigraphy and Microfacies Analyses of The Al Faidiyah ………………………………Faculty of Marine Resources, Alasmarya Islamic University, Libya.During field work the stratigraphic correlation were made in Al Fatiah Cement Quarry (Figure4) this correlation obtained by measure two traverses T1, T2, and T3 is unexposed of the bottom and difficult to tie this term with own correlation (it is doubtful).The datum is lower part of molluskan packstone grading to grainstone microfacies.The correlations between them were constructed in order to identify lateral or vertical lithological changes along the study area.The traverses being correlated are approximately along 700 km from NE-SW.This correlation indicates the following observations :A.Al Faidiyah Formation is recorded in all studied sections, with maximum thickness (about 35 m) as recorded in the Al Fatiah Cement Quarry and generally shows gradual thickness increases toward NE direction.B. The established microfacies have been correlated, considering the base of molluskan packstone grading to grainstone microfacies as datum of this correlation.The upper microfacies is increased towards T2 at SW. On the other hand, the operculinid packstone microfacies laterally changed to algal packstone microfacies at T2.

Figure 4 .
Figure 4. Stratigraphic correlation of Al Faidiyah Formation at Al Fatiah Cement Quarry.
, and El Hawat et al. (2008) by considering the Nummulites fichtelli as reworked elements from the nearby paleohighs.The stratigraphical position as well as the common occurrences of Operculina complanata in the Al Faidiyah Formation at this locality is indicative to Early Miocene.Shaltami et al. (2018a) determined the isotope age for Al E-30 ISSN: 2413-5267Faidiyah Formation, the age derived from the Sr ratios is Early Miocene (Middle Aquitanian, 21.40-22.13Ma).5.Al Huarry Cement Quarry (Benghazi Formation)-Middle Miocene (Late Burdigalian-Early Serravallian)Al Huarry Cement Quarry is represented by 35 m thick sequence of Benghazi Formation.The name was introduced byGregory (1911) as Benghazi limestone for a sequence of massive fossiliferous limestone of Middle Miocene age.Klen (1974) divided Ar Rajmah Formation with in to two members the lower Benghazi Member and the upper Wadi al Qattarah Member and ElHawat and Shelmani (1993) is upranked to Ar Rajmah Group by ElHawat and Abdulsamad, (2004) and raised Benghazi Member to Benghazi Formation based on the recognized hard grounds and rock grounds.The stratigraphic sequence of the studied Al Huarry Cement Quarry has been examined in three as shown in Figure (5).These traverses have been divided into five microfacies which are algae boundstone microfacies, amphisteginid-algae packstone microfacies, amphisteginid grainstone microfacies, algal-bryozan packstone microfacies, and amphsiteginiid-bryozoanalgal boundstone microfacies.

Figure 7 .
Figure 7. Shows Stratigraphic correlation of Benghazi Formation at Al Huarry Cement Quarry.

Figure 8 .
Figure 8. shows a composite columnar section of Al Abyar Quarry.
environment of Al Faidiyah Formation at Al Fatiah Quarry

Figure 10 .
Figure 10.Shows the depositional environment of the study area.