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Abstract The northern Western Desert is the second most important oil-producing area in Egypt. Meanwhile the available geological database specially in the East Yidma oil field was found of very poor quality and insufficient for routine approach, mainly biostratigraphy, paleoecology, and source rock evaluation. The first detail palynological and biostratigraphical studies in addition to the organic geochemical analyses have been presented in the present work. A total of 59 subsurface cuttings samples collected previously by the General Petroleum Company (GPC) from The Drazia-1 well in East Yidma oil field have been selected for this study. The studied intervals comprise three formations: 1) Khoman Formation composed mainly of chalky limestone cherty in the upper most part, 2) Apollonia Formation composed of limestone intercalated with shale and 3) Dabaa Formation composed mainly of shale. The palynologicl investigation in the Drazia-1well, East Yidma concession, north Western Desert, Egypt, have yielded the following conclusions: 1. The palynofacies analysis in the Drazia-1 Well reflects a high abundance of AOM in the Upper Cretaceous succession of Khoman Formation, and high abundance of brown and black phytoclasts in the Eocene-Oligocene succession in Apollonia and Dabaa formations. 2. The statistical analysis based on the ratio of sedimentary organic material groups (palynomorphs, phytoclasts and AOM groups) yielded two playnofacies assemblages (cluster A and cluster B). Cluster A comprises all samples from the depth interval of 4000 to 4990 ft. and is characterized by a relatively high percentage of phytoclasts while cluster B involves the lower interval samples from the depth of 5000 to 5990 ft and is characterized by a relatively high percentage of AOM. 3. The microscopic examination of the studied samples led to the recognition of 154 palynomorph species (115 dinoflagellates, 37 spores, pollen grains and 2 acritarchs species). 4. Five dinoflagellate cyst biostratigraphic zones from Santonian to Oligocene age have been recognized from old to young as following: 4.1. Odontochitina operculata Interval Zone belonging to the age of Santonian to Campanian, from the interval depth of 5990ft. to 5470ft. This zone is extended from the first occurrence of Odontochitina operculata to the first occurrence of Cerodinium diebelii. CONCLUSIONS - 501 - 4.2. Cerodinium diebelii Interval Zone belonging to Maastrichtian age, ranges from the first occurrence of Cerodinium diebelii.at the depth of 5470ft to the FO of Damassadinium californicum. at the depth of 5060ft. 4.3. Damassadinium californicum Interval Zone. (interval from the FO of Damassadinium californicum to the FO of Wetzeliella symmetrica). The age assessment of this zone is Early-Middle Paleocene (Danian-Selandian age), from 5060ft. to 4910ft depth. 4.4. Apectodinium homomorphum Interval Zone. (Late Paleocene-Middle Eocene (Thanetian-Bartonian age). This zone is range from the FO of Apectodinium homomorphum at 4910ft depth to the FO of Deflandrea antaractica at 4710ft depth. 4.5. Deflandrea antaractica Interval Zone., range from the FO of Deflandrea antaractica to the LO of Deflandrea antaractica (4710ft. to 4470ft.interval depth). The age assessment for this zone is Late Eocene-Oligocene (Priabonian- Chattian age). The interval from the depth of 4470ft to 4000ft. have no marker dinocysts ,therefore it is assigned by question mark. 5. The established palynozones have been correlated with equivalent Late Cretaceous- Paleogene dinocyt biozones, locally in Western Desert of Egypt and globally in Eastern New Zealand, Southeastern Australia, Cote dIvoiee, Ghana and Nigeria. 6. The quantity of organic matter in the source rock of Drazia-1 well was evaluated by measuring the amount of TOC, and S2. The organic geochemical and pyrolysis analysis for the selected samples yielded high TOC values ranging from 1.1231 to 1.6956 wt% but the S2 is ranging from 0.66 to 1.36 mg/g, indicate poor source rocks in Khoman, Apollonia and Dabaa formations. 7. The Rock-Eval pyrolysis from the relationships between HI and Tmax . well indicates a kerogen type III. Furthermore, the production index of the Khoman, Apollonia and Dabaa formations ranging from 0.08 to 0.13 indicates immature source rocks. 8. The qualitative and quantitative analysis of the studied interval yielded two palynofacies assemblages, combining with dinocyst group distribution indicate the following two marine environments: 8.1. Shallow marine (Inner neritic environment) for the upper part of the Drazia-1 well (Apollonia and Dabaa formations, depth from 4020 to 4990ft) ranging in age CONCLUSIONS - 501 - from Paleocene to Oligocene, composed mainly of shale intercalated with limestone. It is characterized by a relatively high gamma ray assessment. The calcium carbonate content is ranging from 0.6 to 7.6 wt% in shale and 20 to 67 wt% in carbonate sediments. Almost samples of this interval are located in palynofacies or cluster A which contains enormous amounts of terrestrial translucent and phytoclasts in addition to the sporomorphs. Palynofacies assemblage A is plotting in the AOMphytoclast- palynomorph ternary diagram of Tyson (1995) in fields I and II, that represent a highly proximal shelf or basin (fields I) and Marginal dysoxic-anoxic basin (fields II). 8.2. Deep marine (Middle neritic environment) in the lower part of the studied well (depth from 5000 to 5990 ft) is belonging to the Upper Cretaceous age of Kkoman Formation, composed mainly of carbonate sediments with a calcium carbonate content ranges from 30 to 60 wt% and is characterized by low gamma ray values. The Palynomorph forms suggest that sediments of the Upper Cretaceous were deposited in a relatively deep marine environment. Almost samples in this interval are belonging to palynofacies assemblage B, contain high abundance of AOM (56.6-91.6%) with low abundance of phytoclasts (less than 10%) and low abundance of palynomorphs. Almost samples of this cluster are plotted in the field IX of Tyson (1995) which indicates a shelf setting having suboxic–anoxic conditions. |