Biostratigraphy of the Upper Cretaceous-Lower Eocene succession in the Bani Walid area, northwest Libya

Litho- and planktonic foraminiferal biostratigraphical studies were carried out on the Upper Cretaceous-Lower Eocene succession in three measured sections in the Bani Walid area, northwest Libya. The lithostratigraphical investigations led to the recognition of three formations and six members, from base to top: (i) Zmam Formation, which includes: (a) the Lower Tar Marl Member (Late Cretaceous, Maastrichtian); (b) the Upper Tar Member (Early Palaeocene, Danian); and (c) the Had Limestone Member (Middle Palaeocene, Selandian); (ii) Shurafah Formation, which comprise: (a) the Bu Ras Marl Member; and (b) the Galta Chalk Member (Late Palaeocene, Thanetian); and (iii) Beshima Formation (Kheir Member) of Early Eocene (Ypresian) age. Based on the abundance and stratigraphical distribution of the planktonic foraminiferal species, 12 planktonic foraminiferal zones were recognised, from base to top: Globotruncana aegyptiaca, Gensserina gansseri, Abathomphalus mayaroensis and Plummerita hantkeninoides zones of Late Cretaceous (Maastrichtian) age; Parasubbotina pseudobulloides and Praemurica trinidadensis zones of Early Palaeocene (Danian) age; Praemurica uncinata and Morozovella angulat, as well as Igorina pusilla pusilla zones of Middle Palaeocene (Selandian) age, Globanomalina pseudomenardii and Morozovella velascoensis zones of Late Palaeocene (Thanetian) age and Morozovella formosa formosa zone of Early Eocene (Ypresian) age. The litho- and biostratigraphical results show the presence of two hiatuses in the studied sequence. The first is placed at the Late Cretaceous-Early Palaeocene boundary (K/P boundary) and is located within the Zmam Formation, more precisely at the contact between the Lower and Upper Tar Marl Members and is accompanied by a palaeontological gap, indicated by the absence of the earliest Palaeocene Guembelitria cretacea (P-0) and Parvularugoglobigerina eugubina zones (P-1a). The second one is located between the Late Palaeocene Galta Chalk Member of the Shurafah Formation (Morozovella velascoensis zone) and the Early Eocene Kheir Member of Beshima Formation (Morozovella formosa formosa zone) and is detected by the absence of the Morozovella edgari and Morozovella subbotinae zones, indicating the instability of the study area during Late Cretaceous- Early Eocene times. (C) 2001 Elsevier Science Limited. All rights reserved.