ORIGINAL ARTICLES Ordovician–Carboniferous Palynology of El
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677 Journal of Applied Sciences Research, 9(1): 677-691, 2013 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLES Ordovician–Carboniferous Palynology Of El-Waha-1 Borehole, Western Desert, Egypt. 1Moustafa, T.F, 1Gamal M.A. Lashin and 2Hosny A.M. 1Egyptian Petroleum Research institute, Egypt. 1Botany Department, Faculty of Sciences, Zagazig University, Egypt. 2Geology Department, Faculty of Sciences, El -Azhar University, Egypt. ABSTRACT Diverse acritarchs, chitinozoa, and miospore assemblages were recovered from the Palaeozoic sequence in El-Waha -1 well, north western part of the Western Desert. These assemblages forms have many previously described and well known from the Palaeozoic 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 and less chitinozoans. No miospors have been recorded. The real sporomorphs are recorded only at the upper part of the Silurian with smooth spores (Retusotriletes, Ambietisporites, Archaeozonotriletes), verrucates ones, and Emphanisporites with porrly defined ribs. The 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 phytoplanktons. The Middle Devonian shows the first incoming of small sculptured camerate spores with thick exoexine and large spinate forms related to genera Hystrichospora, Grandisporites and Ancyrosporites . The Early Carboniferous is dominated by vascular plant taxa including laevigate, cingulizonate and cavate forms. No saccate pollen have been recorded in the studied interval. Key wrods: Ordovician; Carboniferous; Palynology; El-Waha-1; Western Desert; Egypt. Introduction Whilst the Mesozoic and Cenozoic rocks of Egypt have been studied in detail because of their economic significance, the Palaeozoic 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 rocks. In the Western Desert, only few previous works on the subsurface Palaeozoic palynology were carried out. The work of Gueinn & Rasul (1986) may consider the most extensive one. They established 15 biozones based on palynomorph assemblage ranging in age from Middle Cambrian to Early Permian. Schrank (1987) identified three assemblages belonging to Silurian, Givetian and Visean from Foram -1 well. El-Shamma et al., (1996) 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 Desert. El- Shamma et al., (1998) established 10 assemblage zones ranging in age from the Lower Devonian to the lowermost Carboniferous from three wells in the Western Desert. The 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 at the longitude 25º 40\ 09\\ E and latitude 30º 33\ 56 N\\ in the north western part of the Western Desert, this borehole was drilled by Epedeco Sallum company in 1998, Material and stratigraphic outline: The regional distribution of the Palaeozoic strata in Egypt shows that there is a thick sequeuce of strata in north west Egypt and a thinner sequeuce in the Gulf of Suez, Sinai area and south west Egypt. Until recently, the Palaeozoic strata of southwest Egypt were undifferentiated due to insufficient stratigraphical evidence. The 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 basement (Klitzch & Lejal – Nicol, 1984). It is unconformably overlain by sandstone of Silurian age. The Silurian is reported from the subsurface of the north Western Desert by (Schrank, 1984) and ( El-Shamma et al, 2003 ). As Corresponding Author: Gamal M. A. Lashin, Botany Department, Faculty of Science, Zagazig University, Egypt. 678 J. Appl. Sci. Res., 9(1): 677-691, 2013 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 Llandovery time. This sea seems to have transgressed into the south west, west and northwest Egypt. Devonian subsurface strata in northwest Egypt were recorded by Schrank (1984) and El-Shamma et al.(1998) through the palynological works. The environment is at least partly marine with a southward increase of continental influence. The 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 forland of one (or several) Devonian transgressions. The 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 country (klitzch & Léjal – Nicol 1984). At the same time northward draining rivers from surrounding areas in the south and southeast filled depressions with fluviatile sediments. The most applicable lithostratigraphic subdivision for the Palaeozoic sequence in the Western Desert we use here is that adopted by Palaeoservices (1986). 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) 112 Ditch samples were obtained from El-Waha-1 well located in the northwestern part of the Western Desert. The samples cover the sequence spanning time interval from the Ordovician to Carboniferous (fig- 1 ) the samples have been subjected to the standard technique of preparation using HF,H Cl and Zn I2 as a heavy liquid separation. Palynostratigraphy: Palynomorphs taxa include (acritarchs, chitinozoan and miospores) have been recorded from all samples. This preliminary investigation of the palynomorph assemblages provide a fairly good indication of age since they include many previously described forms known from the Palaeozoic sediments in different parts of the world. The 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. The recovered assemblage is composed mainly of acritarchs and less chitinozoans. Acritarchs, although they are regularly represented between 3955-3845m they are not diverse. The 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. The upper lithologic interval between 3845 -3765m 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 certitude. No previously data were registered about the Ordovician phytoplanktons in Egypt, and neither Early or Middle Ordovician chitinozoan assemblage has been identified in Libya (Molyneux & Paris, 1985). The 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. The main chitinozoa which were reported include Armerochitina nigerica, Plectochitina sylvanica, Ancyrochitina merga, Belenochitina capilata and Spinochitina sp. 679 J. Appl. Sci. Res., 9(1): 677-691, 2013 Fig. 1: Location map and stratigraphic log of EL-Waha-1 well. The Late Caradoc and Ashgill acritarchs which have been reported from Saudi Arabia by Jachowiez (1995) comprise Ordovicidinium eleganthum, Veryhachium subglobosum, Actinotidiscus crassus and Baltisphaeridium sp.. Almostly this could be match with assemblage of JO-1 Biozone be established by Keegan et al., (1990) from Jordan. The recovered phytoplankton assemblage from the present