ordovician–carboniferous palynology of el-waha-1 borehole...

Indian Journal of Geo-Marine Sciences Vol. 43(8), August 2014, pp. 1484-1499

Ordovician–carboniferous palynology of el-waha-1 borehole, western desert, Egypt

Moustafa, T.F1, Gamal M. A. Lashin,2 Hosny A.M.3& El-Shamma A. A1 1Egyptian Petroleum Research institute Zagazig University, Egypt

2Botany Department, Faculty of Sciences, Zagazig University, Egypt 3Geology Department, Faculty of Sciences, El -Azhar University, Egypt

(E-mail: [email protected])

Received 9 September 2012; revised 25 February 2014

Diverse acritarchs, chitinozoa, and miospore assemblages were recovered from the Paleozoic sequence in El-Waha -1 well, north western part of the Western Desert. Assemblages have many previously described forms known from the Paleozoic strata in north Gondwana and other parts in the world. The study revealed that the sedimentation was repeatedly interrupted , as is confirmed by stratigraphic breaks. It revealed also that the Ordovician assemblage as well as the lower part of the Silurian are composed mainly of acritarchs, less chitinozoans and no miospores have been recorded. Real sporomorphs are recorded only at the upper part of the Silurian with smooth spores (Retusotriletes, Ambietisporites, Archaeozonotriletes), verrucates ones, and Emphanisporites with poorly defined ribs. Early Devonian is characterized by zonate – camerate, pseudosaccate, a relatively simple spore types and verrucate ones, that is beside a considerable increase in diversity of the phytoplankton. Middle Devonian shows the first incoming of small sculptured camerate spores with thick exospores wall and large spinate forms related to genera Hystrichospora, Grandisporites and Ancyrosporites. Early Carboniferous is dominated by vascular plant taxa (Ferns) including laevigate, cingulizonate and cavate forms. No saccate pollen grains (Gymnosperms) have been recorded in the studied interval.

[Keywords: Carboniferous –Ordovician- El-Waha-1-Palynology, Western Desert, Egypt.]

Introduction

Whilst the Mesozoic and Cenozoic rocks of Egypt have been studied in detail because of their economic significance, the Paleozoic rocks have received little attention and therefore, the least understood sequence in the area. These rocks have sporadic faunal assemblage which are not useful in age dating, that is why palynology became urgent useful in dating and solving the correlation problem for this part of the Western Desert. The earlier palynological studies in Egypt have been initiated on the Gulf of Suez and Sinai and have concentrated in the Carboniferous rocks1. In the Western Desert, only few previous works on the subsurface Paleozoic palynology were carried out. The work of1 may consider the most extensive one. They established 15 biozones based on palynomorph assemblage ranging in age from Middle Cambrian to Early Permian.2 identified three assemblages belonging to Silurian, Givetian and Visean from Foram-1 well3,4. recognized five broad-based palynological units ranging in age from Early Visean to Early Permian in two wells (NWD - 302-1 and Faghur-1) located in the north Western Desert5

established 10 assemblage zones ranging in age from the Lower Devonian to the lowermost Carboniferous

from three wells in the Western Desert. Present study may consider a continuous trial to shed light about the palynological characteristics of this mistrial succession through the data available from El-Waha-1 well located in the north western part of the Western Desert.

The regional distribution of the Paleozoic strata in Egypt shows that there is a thick sequence of strata in north west Egypt and a thinner sequence in the Gulf of Suez, Sinai area and south west Egypt. Until recently, the Paleozoic strata of southwest Egypt were undifferentiated due to insufficient stratigraphical evidence. Ordovician strata are identified in Karkor Talh in the northeastern part of Gebel Oweinat and the Egyptian–Sudan border. This consists of shallow marine sandstone directly above Precambrian basement7. It is unconformably overlain by sandstone of Silurian age. The Silurian is reported from the subsurface of the north Western Desert by8,3. As in Ordovician time, Egypt was during the Silurian near the eastern edge of the sea which covered a large area of north Africa and reached its maximum extension during Llandoverian time. This sea seems to have transgressed into the south west, west and northwest Egypt. Devonian subsurface strata in northwest Egypt

MOUSTAFA et al: EL-WAHA-1 BORE HOLE WESTERN DESERT, EGYPT

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were recorded by8,4. through the palynological works. Environment is at least partly marine with a southward increase of continental influence. Devonian sediments of western Abu Ras Plateau and of northeast Gebel Oweinat are compared with the Tadrat Sandstone Formation of Libya. It's certainly a fluviatile sediment deposited in the southern and eastern to southeastern foreland of one (or several) Devonian transgressions. Carboniferous sediment strata of Egypt differ in facies, and range from fully marine carbonate, shale and deep marine clastics, deltaic and continental fluviatile sandstone to lacustrine and fluvio- glacial deposits. This may due to the structural development of that time. Until late Visean or Namurian, Egypt was at the southern edge of a more or less shallow sea which transgressed parts of the country7. At the same time northward draining rivers from surrounding areas in the south and southeast filled depressions with fluviatile sediments. Most applicable lithostratigraphic subdivision for the Paleozoic sequence in the Western Desert we use here is that adopted by9. This classification seems to be acceptable by Egyptian General Petroleum Corporation (EGPC) and Oil Companies and includes two formal lithostratigraphical groups. They can also be readily subdivided into formations on the basis of gross lithology:

A-Siwa Group (Early –Mid. Cambrian–Late Silurian)

1-Shifah Formation (Mid. Cambrian–Mid. Ordovician) 2-Kohla Formation (Late -Llandoverian-Ludlovian) 3-Basur Formation (Mid–Late Ludlovian)

B-Faghur Group (Early Devonian–Early Permian)

1-Zeitun Formation ( Gedinnian–Late Devonian) 2-Desouqy Formation (Tournaisian–Visean) 3-Dhiffah Formation (Late Visean–Late Namurian) 4-Safi Formation (Late Namurian–Early Permian)

Materials and Methods

One hundred twelve (112) Ditch samples were obtained from El-Waha-1 well located in the northwestern part of the Western Desert. Samples cover the sequence spanning time interval from the Ordovician to Carboniferous (Fig. 1). Samples have been subjected to the standard technique of preparation using HF, Hcl and Zn I2 as a heavy liquid separation10

. Results And Discussion

Palynostratigraphy Palynomorphs taxa include (acritarchs, chitinozoan

and miospores) have been recorded and identified from all studied samples (Plates 1-5). This preliminary

Fig. 1Location map (A) and stratigraphic log of EL-Waha-1 well (B).

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PLATE IFig. 1: Rhabdosporites minutes (Balme) Playford. Fig. 2: Cymbosporites proteus McGregor & Camfield. Fig. 3: Stenozonotriletes simplex Naumova. Fig. الفنانة اللبنانية رزان المغربيverrucatus Richardson & Ioannides. Fig, 7: Archaeozonotriletes sp. Fig. 8: Aneurospora sp. Fig. 9: Dibolisporites sp. Fig. 10: Retusotriletes cf. communis Naumova. Fig. 11: Dibolisporites eiflelinsis (Lanninger) McGregor. Fig. 12: Synorisporites Lybicus. Richardson & Ioannides. Fig.13: Apiculiretusisporites plicata (Allen) Streel. Fig. 14: Craspedispora sp. Fig. 15: Brockotriletes sp. Figs. 16, 22: Emphanisporites rotatus McGregor. Fig. 17: Emphanisporites erruticus Eisenack. Figs. 18, 19: Dictyotriletes emsiensis (Allen) McGregor. Fig. 20: Emphanisporites sp. Fig. 21: Emphanisporites annulatus McGregor. Figs. 23, 24: Emphanisporites spinaeformis Schultz. Fig. 25: Emphanisporites abscurus McGregor. Fig. 26: Verrucosisporites scurrus (Naumova) McGregor & Camfield. Fig. 27: Lophozonotriletes sp.


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PLATE IIFig. 1: Brockotriletes hudsonii McGregor & Camfield. Fig. 2: Dictyotriletes emsiensis (Allen) McGregor. Fig. 3 Endosporites micromanifestus Hacquebard. Fig. 4: Hymenozonotriletes discors Chibrickova. Fig. 5: Comptozonotiletes caperatus McGregor. Fig. 6: Spelaeotriletes cf. crustatus Higgs. Fig. 7: Geminospora lemurata (Balme) Playford. Fig. 8: Verrucosisporites polygonalis Lanninger. Fig. 9: Apiculiretusisporites brandti Streel. Fig. 10: Grandispora protea (Naumova) Moreau Benoit. Fig. 11: Ancyrospora acutispinosa Chi & Hills. Fig. 12: Ancyrospora longispinosa Richardson. Fig. 13: Grandisporites libyensis Moreau Benoit. Fig. 14: Grandispora inculta Allen. Fig. 15: Camarozonotriletes sp. Fig. 16: Diatomozonotriletes sp. Fig. 17: Synoriporites papillensis McGregor. Fig. 18: Verrucosisporites premnus Richardson. Fig. 19: Aratrisporites sahariensis Loboziak & Alpern. Fig. 20: Rugospora flexuosa (Jushko) Streel. Fig. 21: Dipolisporites echinaceus (Eisenack) Richardson. Fig. 22: Verrucosisporites nitidus (Naumova) Playford.


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PLATE IIIFig. 1: Spelaeotriletes owensi Loboziak & Alpern. Fig. 2: Vallatisporites agadesi Loboziak & Alpern. Fig. 3: Spelaeotriletes triangulus Neves & Owens. Fig. 4: Radiizonates genuinus Loboziak & Alpern. Fig. 5: Vallatisporites pusillites (kedo) Dolby & Neves. Fig. 6: Vallatisporites verrucosus Playford. Fig. 7: Spelaeotriletes benghaziensis Loboziak & Alpern. Fig. 8: Spelaeotriletes arenuceus Neves & Owens. Fig. 9: Umbonatisporites sp. Fig. 10: Retusotriletes crassus Clayton, Johnston, Sevastogolo & Smith. Fig. 11: Vallatisporites ciliaris (Luber) Sullivan. Fig. 12: Spore type A Clayton &Loboziak. Fig. 13: Convulatisporites cf. mellita Hoffmeister, Staplin & Malloy.


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PLATE IVFig. 1: Veryhachium lairdi Cramer. Figs. 2, 11: Micrhysphaeridium stellatum Deflandre. Figs. 3, 12: Ononadagella asymmetrica (Deunff.) Cramer. Figs. 4, 10, 15, 16: Baltisphaeridium spp. Fig. 5: Diexallophasis caperoradiola Lioblich. Fig. 6: Veryhachium trispinosum (Eisenack) Deunff. Fig. 7: Veryhachium downei Stockmans & Willieri. Fig. 8: Diexallophasis remota (Deunff) Playford. Fig. 9: Triangulina alargada Cramer. Fig.13: Cymatiosphaera perimembrana Staplin. Fig, 14, 20: Polyedriyxium carnatum Playford. Fig.17: Navifusa bacillum (Deunff) Playford. Fig. 18: cf. Baltisphaeridium sp. fig. 19: Actinotidiscus crassus Loeblich & Tappan. Fig. 21: Cymatiosphaera sp. Fig. 22: Timofeevia lancarae (Cramer & Diez) Vanguestaine.


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PLATE VFig. 1: Ancyrochitina sp. Fig. 2: Ancyrochitina tumida Taugourdeau & Jekhowsky. Fig. 3, 9: Ancyrochitina cornigera Collinson & Scott. Fig. 4: Angochitina cullinsoni Taugourdeau & Jekhowsky. Fig. 5: Ancyrochitina spinosa Eisenack. Fig. 6: Ancyrochitina capillata Eisenack. Figs. 7, 8: Ancyrochitina ancyrea Eisenack. Figs. 10, 11: Angochitina devonica Eisenack. Fig. 12: Fungochitina pilosa Collinson & Scott. Fig. 13: Desmochitina sp. Fig. 14: Ancyrochitina desmia Eisenack. Figs. 15, 19: Belenochitina sp. Fig. 16: Angochitina sp. Fig. 17: Conochitina sp. Fig. 18: Desmochitina aranea Urban. Fig. 20: Conochitina inflate Wood.


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investigation of the palynomorph assemblages provide a fairly good indication of age since they include many previously described forms known from the Paleozoic sediments in different parts of the world. Occurrence of the taxa in the studied samples and their stratigraphic range were plotted in Figs., 2, 3 and 4.

Ordovician (interval from 3970 to 3765 m) No sporomorphs have been recorded within this

stratigraphic interval. Recovered assemblage is composed mainly of acritarchs and little number of chitinozoans. Acritarchs, although they are regularly represented between 3955-3845 m. and they are not diverse. Main species here are Visbyosphaeridium

subglobosum, Veryhachium sp., Ordovicidinium sp., Timafeevia lancarea, Solisphaeridium sp. and Actinotidiscus crassus. Chitinozoa are represented by Plectochitina sylvanica and Belenochitina sp. Upper lithologic interval between 3845-3765 m is barren.

The published acritarchs data for the Ordovician are still somewhat sparse and for this reason, there are several difficulties to establish the real stratigraphic significance of the taxa recorded with exception of very diagnostic species for which the biostratigraphy seems to be known with certitde.

No previously data were registered about the Ordovician phytoplankton in Egypt, and neither Early or Middle Ordovician chitinozoan assemblage

Fig. (2)Stratigraphic distribution of the Ordovician-Silurian palynomorphs in El-Waha-1 well.


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has been identified in Libya11. Late Ordovician acritarchs which have been identified by these authors are dominated by Veryhachium spp. with Navifusa similis, Ordovicidinium heteromorphicum, Actinotidiscus cf. crassus, Leiofusa sp. and Eupoikilfusa striata. Main chitinozoa which were reported include Armerochitina nigerica, Plectochitina sylvanica, Ancyrochitina merga, Belenochitina capillata and Spinochitina sp.

Late Caradoc and Ashgill acritarchs which have been reported from Saudi Arabia by12 comprise Ordovicidinium eleganthum, Veryhachium subglobosum, Actinotidiscus crassus and Baltisphaeridium sp.. All mostly this could be match

with assemblage of JO-1 Biozone be established by13 from Jordan. The recovered phytoplankton assemblage from the present study could be more or less comparable with those data and be referred to the same age (Late Ordovician). Diversification in species taxa, as well as long ranging interval of some of them and lithofacies control make the determination of the precise age for the studied interval is difficult process. Silurian (interval from 3765 to 3200 m)

This thick stratigraphic succession with its different lithology shows extremely variation in its palynological content. Lower interval between

Fig. (3)Stratigraphic distribution of the Devonian palynomorphs in El-Waha-1 well.


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3765–3710 m. has only few chitinozoa species represented by Conochitina inflate and Ancyrochitina sp.. Interval between 3710–3560 m is barren from any palynomorphs, meanwhile the interval between 3560–3440 m.is rich with acritarchs and sporadic occurrence of Ancyrochitina sp.. Most represented acritarchs herein are Micrysphaeridium sp., Eupoikolifusa striatifera, Visbyosphaeridium subglobosum, Baltisphaeridium sp., Veryhachium lairdi, V. trispinosum, Diexallophasis remota, D. denticulatus, Polyedryxium carnatum and Onondagella deunfi. Chitinozoa are relatively increase upward and represented mainly by Eisenachitina sp., Ancyrochitina

ancyrea and Fungochitina pilosa. At sample 3440 m and upward; spores show their first record and represented by Retusotriletes goensis, R. aviatus, Archaeozonotriletes chulus, Ambietisporites dilutes, Synorisporites verrucosus, and Emphanisporites neglectus. Many of these taxa have not been recorded in rocks younger than the Upper Silurian sequence elsewhere.

This palynomorphs assemblage are closely comparable with that reported by4 from the Llandoverian strata of NWD-302-1 well in the Western Desert, Egypt. A similar assemblage has been also recorded by1 from Llandoverian-Ludlovian age zone

Cont. Fig. (3)Stratigraphic distribution of the Devonian palynomorphs (Acritarchs and Chitinozoa) in El-Waha-1 well.


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WD-5 of Egypt and by14 from Tanezzoft and Accacus formations of Libya. Record shows somewhat earlier occurrence of verrucate spores (Synorisporites) and Emphanisporites with poorly defined ribs (E. neglectus, E. micrornatus) which present in strata of probably Early-Middle Ludlovian age. Emphanisporites rotatus and Apiculate retusoid spores only occur near the top of the Libyan section. A similar spore assemblage has been reported by16 within the “Synorisporites tripapillatus–Apiculiretusispora specula” assemblage zone of Downtonian age of the Old Red Sandstone Continent and adjacent regions.

An acritarchs assemblage with Veryhachium trispinosum, Diexallophasis caperoradiola, Visbyosphaeridium sp. and Cymbosphaeridium sp. with chitinozoa of Sphaerochitina sp., Angochitina sp., Conochitina adjelensis, Cyathochitina sp. and spores of Archaeozonotriletes cf. chulus, Ambietisporites dilutes and Dyadospora spp. were reported from the Silurian of Libya by12 Onondagella deunfi has a known age spanning the Silurian to Early Devonian in north Africa, that is beside Archaeozonotriletes spp. and Emphanisporites spp.17. It is worthy to mention that there are some difficulties in using acritarchs for interregional correlation since the geographic distribution of them is considerably influenced by local environmental factors. From the foregoing discussion, we can’t conclude a precise age for the lower part of the studied interval depending on their phytoplankton content, mean while the upper part which bear spores and regular occurrence of acritarchs could be referred to Late Silurian (Llandoverian -Ludlovian). Siegenian (Pragian)-Early Emsian (interval from 3200 to 2855 m)

preliminary palynological investigation of this stratigraphic succession could be subdivided into two assemblages. The first one is recorded between interval 3200–2930 m. and characterized by spores Calyptosporites sp., Synorisporites verrucosus, Dictyotriletes sp., Ambietisporites sp., Brockotriletes hudsonii and a variety species of genus Emphanisporites (E. rotatus, E. erruticus, E. neglectus , E. spinaeformis and E. obscurus). Upper assemblage between 2930–2855 m. shows the first occurrence of Rhabdosporites langi, Apiculiretusisporites brandti, Verrucosisporites permnus, V. eifeliensis and Emphanisporites annulatus. That is beside most of the pre-mentioned taxa from the lower assemblage.

Acritarchs show a regular occurrence and represented mainly by Micrysphaeridium stellatum, Gorgonisphaeridium sp., Diexallophasis remota, Polyedryxium carnatum, Veryhachium downei, V. trispinosum, Trigulina alargada, Cymatiosphaeridium perimembrana, S. pilaris, Onondagella asymmetrica and Baltisphaeridium sp. Chitinozoa species are relatively few and mostly represented by Ancyrochitina desma, A. ancyrea, A. cornigera, A. tumida, A. longispinosa, Fungochitina pilosa, Lagenochitina sp., Angochitina sp. and Conochitina inculta. The recovered assemblage in general is demonstrated by many species known to range from the upper part of the Early Devonian into the Middle Devonian and occasionally occur in even younger strata. Furthermore, zonate-camerate spores (Camptozonotriletes) have not been reported from well-dated strata older than Siegenian. Dibolisporites eifeliensis first occurs in Siegenian rocks but only become abundant in the Emsian6 reported Verrucosisporites polygonalis–Dictyotriletes emsiensis, assemblage zone for the Siegenian of the Western Desert, Egypt. They assigned Emphanisporites annulatus–Camarozonotriletes sextantii assemblage zone to the Emsian. Absence of real Emsian taxa such as Grandispora velata, G. nettersheimensis, G. douglastownense, G. mamillata and Ancyrospora acutispinosa indicate that the age may be referred to early Emsian18 indicated that Verrucosisporites polygonalis and Dictyotriletes emsiensis are represented among a typical Upper Siegenian-Lower Emsain assemblage in Canada19 mentioned that Retusotriletes, Apiculiretusisporites and Emphanisporites with not developed ribs (Emphanisporites rotatus and E. neglectus) are the most genera in the Siegenian of southern Britain20 reported Dictyotriletes emsiensis, Dibolisporites eifeliensis, Brochotriletes sp., Emphanisporites spinaeformis and Aurorospora micromanifestus, with chitinozoa Angochitina devonica, Ancyrochitina langi, and A. ancyrea of Late Siegenian-Early Emsian age of Libya21 mentioned some facts about the Emsian spores;

(1) Dibolisporites eifeliensis has not been recorded before the Lower and Middle Emsian.

(2) Emphanisporites erruticus is unknown before the top of the Lower Emsian.

(3) Ancyrosporites and Hystrichosporites are absent in the lower part. They do not occur before Upper Emsain together with


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pseudosaccate and zonate spores in the upper most Emsian22,23 mentioned too that spores of Ancyrosporites nettersheimensis and Hystrichosporites microancyreus occur first at about Mid-Late Emsian age. The same conclusion has been mentioned by24 from the Denant Basin.

Emphanisporites annulatus begins in south west Eifel in the lower part of Upper Emsian 25 and at probably Middle Emsian at Gaspe Bay26 and probably Emsian.24,26, concluded that the specimens of Grandisporites douglastwense, G. macrotuberculata and Dibolisporites echinaceus appear at the middle of Upper Emsian. In this respect, it seems appropriate to note that the Siegenian/Emsian boundary may occur in the present interval but it is difficult to locate it.

Position of the boundary itself has not been defined, since no obvious changes in composition of the spore assemblage could be detected through the present interval. This interval is thus included in an undifferentiated palynostratigraphic unit of Siegenian/ Emsian time.

Eifelian (interval from 2855 to 2630 m) The recovered assemblage from this stratigraphic

interval shows an extinction of some characteristic Emsian spores such as Rhabdosporites langi, Brochotriletes hudsonii and Apiculiretusisporites brandti; other new characteristic forms show their first incoming such as; Grandisporites douglastwense, G. nettersheimensis, G. libyensis, Spinozonotriletes naumovi, S. langii, Hystrichosporites bifurcata, H. gravis, H. longispinosa and Hymenozonotriletes

Fig. (4)Stratigraphic distribution of the Carboniferous miospores in EL-Waha-1 well.


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discors. Marine chitinozoans and acritarchs still persisting and represented by most of the Emsian taxa although they are less abundant. Recorded assemblage is characterized by a proliferation of the large apiculate and spinulose, zonate-pseudosaccate spores (Grandispora, Hymenozonotriletes, Rhabdosporites and Spinozonotriletes). All of these are typical Middle Devonian taxa.7 reported that the Eifelian palynomorphs of Faghur-1 and NWD-302-1 wells, Western Desert are characterized by occurrence of Hymenozonotriletes discors, Grandispora inculta, G. velata, Veryhachium trispinosum, Diexallophasis caperoradiata, Fungochitina pilosa, Angochitina devonica, Ancyrochitina tumida, A. desma and Alpenachitina cornigera. An assemblage with Hystrichosporites spp., Grandisporites libyensis and Ancyrosporites nettersheimensis has been reported from Eifelian sediments by20,35 from Libya. This is closely comparable with those recorded by27 from Algeria, and by28 from Saudi Arabia29 recorded an assemblage with Grandispora riegeli, Emphanisporites annulatus, Acinosporites lindlarensis, Verrucosisporites premnus and V. scurrus. Saudi assemblage was recorded from beds of uncertain age but it thought to be of Eifelian age based apparently on its stratigraphic position. Recovered assemblage here could be also related to zone “G. douglastwense –A. eurypterata”16 of Eifelian age. It should be mention here, that the data available for comparison indicated that the Eifelian assemblage of the present study has more in common with those from the north African region rather than those from elsewhere.

Givetian (interval from 2630 to 2555 m.) An abrupt change both in the quantity and diversity

of taxa has been recorded within this interval. Most of the previously recorded taxa have been distinct. Main represented spores herein are Retusosporites spp., Grandisporites inculta, Ancyrosporites acutispinosa, Geminospora lemurata and Hystrichosporites gravis . Marine acritarchs and chitinozoans are represented sporadically with few long-ranging forms related to genera Veryhachium, Polyedryxium, Diexallophasis, Fungochitina and Conochitina. The first occurrence of small sculptured camerate spores with a thick exoexine such as Geminospora lemurata and its related species is regarded as the most spore marker to locate the base of the Givetian stage30. Most-if not all –of these recovered taxa were reported by7, from Fig.-1 and NWD-302-1 wells in the Western Desert, of Egypt and assigned to the Givetian age. Recovered assemblage

carries also the general characteristic features of the Givetian microflora encountered in Libya by31 and 32,33,34,35. A corresponding Givetian spores assemblages “Densosporites devonicus–Grandisporites naumovi” and “Geminospora lemurata-Cymbosporites manificus” zones suggested by 16 are rich with Grandispora, Ancyrospora, Rhabdosporites and Aneurospora. Other data available from many localities of the world indicates that the Givetian assemblage of the Egyptian Western Desert is generally similar to those recorded from the Old Red Sandstone continent and adjacent regions16, Poland36,37, Shetland38, Canada18 ,39, and from the Parana Basin; Brazil 40.

Carboniferous: Visean (interval 2555-2230 m) The dominant fraction of the organic matter of this

stratigraphic interval is of continental origin. Miospores are abundant, most of them belong to smooth (Retusotriletes), apiculate (Apiculiretusitriletes) to verrucate (Verrucosisporites sp.) as well as to a variety of genera Densosporites, Radiizonotes and Vallatisporites. Palynological association of this stratigraphic interval could be subdivided into two interfered assemblages, both is related to the Visean age since they have many shared taxa, at the same time some different palynological events are observed.

Early Visean (interval 2555-2335 m) The assemblage recorded herein is characterized by

some important taxa include; Lycospora pusilla, Densosporites annulatus, D. spiniferites, Vallatisporites vallatus, V. verrucosus, V. nitidus, Raistrickia spatulata, Spelaeotriletes arenaceous, S. balteatus, Diatomozonotriletes fragilis, Radiizonates genuinus, Convulatisporites mellita, Aratrisporites sahariensis. that is besides other spores belonging to genera Punctatisporites. Calamaspora, Retusotriletes, Granulatisporites and Umbonatisporites. Most, if not all, these microfossils were recorded from the Lower Visean sediment of NWD–301-1 well by3 and included in WD-13 zone which was suggested by1. The assemblage has shared species with zone (II) of Visean age assigned by 15 Um Bogma, Sinai such as Punctatisporites spp., Retusotriletes sp., Verrucosisporites sp., Convulatisporites sp., and Calamaspora sp. and with zone (A) of Visean from central Sinai by41. A similar assemblage of Early Visean age has been noted by42, and43, from north east Libya,35 from Al-Kufra Basin of south east Libya,44 in Algeria,45 from Brazil,37 from northern Niger, and47 from Amazon Basin, northern Brazil.


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Late Visean (interval 2335-2230m.) Many taxa from the preceding age are common

elements herein particularly; Aratrisporites, sahariensis, Lycospora pusilla, Vallatisporites vallatus, Verrucosisporites nitidus, Radiizonates genuinus and Diatomozonotriletes agilis. Other species have their real occurrence in this stratigraphic interval such as; Spelaeotriletes triangulus, S. owensi, Vallatisporites agadesi, V. ciliaris, Raistrickia clavata and R. spatulata.48 established Zone-I from Wadi Araba with spores Punctatisporites sp. Raistrickia sp., Densosporites sp. and Convulatisporites sp. which are dated as Late Visean, the same association has recovered also by1,4,8 in Egypt. In north Africa, the first occurrence of Lycospora pusilla was considered by20,43 and48to occur only in Late Visean.

The recovered assemblage could be correlated too by those reported by42 in Libya,44 from Sahara Algeria, and by 47 from northern Brazil. Early Namurian (2230–2125 m)

Miospores recovered within this stratigraphic interval are distinguished by the flourishing of smooth types (Calamaspora, Retusotriletes, Punctatisporites), apiculate (Apiculiretusispora spp.) and cingulicavate forms as Vallatisporites and Spelaeotriletes. Most characterizing taxa represented here are Vallatisporites ciliaris, Spelaeotriletes benghaziensis and S. owensi. That is besides many of Visean forms related to genera Granulatisporites, Convulatisporites, Densosporites, Diatomozonotriletes and Radiizonates.

This assemblage is similar to that recorded in WD-13 and WD-14 zones of2 by the presence of Spelaeotriletes owensi, S. arenaceous, Lycospora pusilla and absence of monosaccate pollen. The same conclusion is mentioned by1 and48 . Assemblage is also correlated with miozone (ΙΙΙ) of Early Namurian assigned by4 from NWD-302-1, Faghur-1 and west Faghur-1 wells, Western Desert specially in presence of Densosporites spp., Spelaeotriletes triangulus, S. benghaziensis Vallatisporites verrucosus, Diatomozonotriletes fragilis, Vallatisporites agadesii and Calamaspora sp. Serpukhovian age which noted by20 from Libya comprises Lycospora pusilla, Vallatisporites ciliaris and Spelaeotriletes triangulus. Same conclusion was mentioned by42 and by43 and from north Niger by46 and referred to early Namurian. Conclusions

The present study revealed that, the sedimentation in the present borehole was repeteadly intrupted, as inconfermed by stratigraphic breaks between different ages. Some of these breaks are matching with the general structural breaks in the stratigraphy of Egypt and north Africa such as that between the Ordivician/Silurian, Silurian/Devonian and Devonian/Carboniferous. Other breaks may be cosidered as local stratigraphic ones represented by decreasing in thickness of some ages or their competely absences. Diversification in acritarchs species recorded in many correletable areas, as well as, along ranging intervals of some of them and lithofacies control prevent determination of the precious age of some studied intervals such as the Ordovician and Silurian. An abrupt change in palynomorph diversity between the Eifelian and Givetian was recorded as indicated by the proliferation of large spinate spores in the Givetian. No saccate pollen have been recorded in the studied Carboniferous interval, at least at the beginning of the Namurian age. References

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ordovician–carboniferous palynology of el-waha-1 borehole...

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