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Abstract and bio stratigraphy of the Eocene succession exposed in Helw an area. few kilometer s to south of Cairo . Six stratigraphic sections were collected and studied representing Middle and late Eocene ages. These sections from north to south are as follows: Observatory , East Observatory. Ochsen Rid ge, Sunken Hillock. Wadi Garaw i and Qurn sections. The rock unit s composing the studied sections are from oldest to youngest as follows: Gebel Hof (’topmost part ). Observatory. Qurn , Wadi Garawi and Wadi Hof Formations.The Gebel Hof Formation ( topmo st part) together with Observatory and Qurn Formations are considered (Middle Eocene) to be of Bartonian age, on the other hand , the other two Formations ; namel y Wadi Garawi and Wadi Hof Formation s of Late Eocene, Priabonian age . The distribution of the larger foraminifer al species enabled to subdivide the strati graphic sequen ce into three Biostratigraphi c assemblage zones, these Biostratigraphic units are from base to top as follows: I -Dictyocollus aegyptiensis I Idalina cuvillieri Assemblage zone : In addition to the marker species the followin g speci es are recorded : N.sp .cf. hollingeri. N.b ullalus and Lockhar tia c[ haimei. This zone attains a thickness of about 14 m. 1t span s the topm ost exposed part of Gebel Hof Formation at Ochsen Ridge section . This zone i s assigned to Bartonian age 2- N ummulites aff.pulche/lus I Nmmu lites beaumonti Assemblage Zone: Besides th e mark er speci es the followin g species are record d : N.b ufla tus .N.beaumomi, N. cf beaumonti, N. sp.c[h olling eri. N.dis corbinus. D ictyoco nus aegyptiensis and spha erogypsina g lobula. This zone attains a thickne ss ranging from 90 to 145m 1t span s the Observatory and Qurn section . This zone is assigned to Bartonian age. 3- N ummulites striatus Range Zone This zone attains a thickness of bout 16 m .It characterizes Wadi Garawi and Wadi HofFormations .This zone is considered to be of Priabonian age according to SCHAUB’S Nu mmuli tic Scale. The present stud y prooved that the lithostrati graphic classifi cati on of the Eocene sequence in Helwan FARAG & ISMAIL ( 1960) bel ongs to the Eastern Desert facies representing restricted marin e en viron ment especial y during the Bartonian wh ich is distinct and separated from the Mokattam facies. |