Egypt. Jou r. Paleontol., Vol. 2, 2002, p. 371-384 PALYNOLOGY AND PALAEOENVIRONMENT OF THE BAHREIN FORMATION, ZEITUN-1 WELL, WESTERN DESERT, EGYPT Salah Y. EL BEIALY '", Abdel Fallah A. ZALAT 1 21 , Ali S. ALI 12) (1) Geology Department , Faculty of Sci ence , EI Man soura Univ ersity, EI Ma nsoura, 35516, Eg ypt. syelbei aly@ ma ns.edu.eg (2) Geology Depa rtment, F aculty of Sci ence , Tanta University, Fanta 3 1527, Egypt , azalat @dec1.tanta .edu.eg; asoliman @dec1 .tanta.edu.eg ABSTRACT A diverse, pteridophytic (tem)-dominated, palynomorph assemblage was recovered Irom the subsurface section 01 the Bahrein Formation, Zeitun-1 Well. Both miospores and dinoflage llate cysts correlate well with several Bajocian - Bathonian associations Irom the local and worldwide palynological records . Crassiludisporiles problematlcus , Siaplinisporites caminus. Neoraistrikia lruncata, Malonisporites crassiangulalus, Baculatisporites comaumensls and Leptolepidiles bossus are stratigraphically significant miospores , Although dinoflagellate cysts are minor constituents or me palynomorph content, they encounte red Adnatosphaeridiun caul/aryl and Ctanidodinlum omalum that are of considera ble stratigraphic potential. The dominance of terrestrially-d erived pollen and spores together with the sporadic and intermittent occurrence of marine dinoflagellate cysts and microforaminiferallini ngs suggest continental to marginal (coastal) marine palaeoen vironment. The remarkable abundance of the pteridophytic fern spores with other hygrophilous elements indicates warm humid palaeoclimate during deposition of most of the Bahrein Formation section, A horizon of the borehole section witnessed a notable retreat in the frequency of ferns, associated With the most frequent xerophytic elements (Classopollis) . This implies that an arid episode occurred, INTRODUCTION Subsurface Jurassic sediments in the northern Western Desert , Egypt form an important objective since the 1985 discovery of hydrocarbon reservoirs (Khalda Petroleum's, Salam 3X well). Most of the earlier published palynological works have focused on miospores, since palynomorphs are the most abundant among other microfossil groups (e.g. Abdel Malik et al. 1981, Bassiouni et al. 1981, Schrank 1984, 1987, 1991; Mahmoud 1991, Mahmoud & Moawad 2000, Ali 2000 and Abdel Mohsen et al. 2001). The Bahrein Formation was introduced by WEPCO to describe the subsurface continental Jurass ic sediments , which underly the marine Jurassic strata in several Western Desert localities (Hanter 1990, Issawi et at 1999). In the Zeitun-1 Well, the formation is composed of fine to medium-grained white to whitish grey sandstone, rarely kaolinitic with sandy shale intercalations in the upper part. White, fine-grained sandstone with minor brown sandy shale intercalations was recorded in the lower part. Continental Mesozoic sediments are widely distributed in Egypt and in other parts of the world. In such sediments, palynology has contributed extensively to the understanding of their palaeoenvironmental characteristics. Land-derived pollen and spores are transported to the marine realm; they can be used to correlate contemporaneous continental and marine successions. This is one of the advantages of the study of terrestrial palynomorphs . It is worthy noting that, unless otherwise reworked , marine palynomorphs (e.g dinoflagellate cysts) can not be transported further in land. The present study aims to investigate the palynomorphs from the Bahrein