engleski

Eocene/Oligocene boundary (Vacus Member) in the western part of the Tripolitania basin, Libya

Exploration well NC-167 in the western part of the Tripolitania Basin (Libya) was drilled through Eocene and Oligocene deposits. Eocene limestones. They contained a poor microfossil sediments are predominantly clayey and sandy wackestone type association, typical of lagoons with high salinity and weak aeration, where only ostracods and rare benthonic foraminifera survived. At the top of Eocene a few specimens of Nummulites sp. appear with small benthonic foraminifera including Nummulites trumpy (Nuttall), Bulimina alazanensis Cushman, Cibicides lobatulus (Walker and Jacob) and Planulina renzi Cushman and Stainforth. Planktonic foraminifera are rare or absent, but the appearance of Turborotalia cocoaensis (Cushman) is significant for stratigraphic determination. In the Early Oligocene gray to white packstone (biomicrites) prevail which contain a great amount of shells of larger foraminifera with dominant species Nummulites vascus (Joly and Leymerie). Besides this species, smaller benthonic foraminifera (Planulina, Asterigerina, Cibicidoides), corallinaceans and echinoid debris have been observed. These Early Oligocene sediments were deposited in the restricted shallow shelf environment. This horizon (known as Vascus member) is very useful for recognition Eocene/Oligocene boundary in the wider region (Libya, Tunisia). Planktonic foraminifera in similar shallow paleoenvironments are almost absent. Above the boundary Nummulites fichteli Michelotti, Operculina complanata (Defrance) and first appearance of lepidocyclines have been found

foraminifers; stratigraphy; tertiary

nije evidentirano