Biostratigraphy of Palaeocene to Miocene Foraminifera in Concession 65, SE Sirt Basin, Libya

Abstract

Palaeocene to Miocene planktic and larger benthic foraminifera retrieved from ditch cuttings samples taken from 5 wells drilled in Concession 65, SE of Sirt Basin, Libya, have been studied biostratigraphically. This study indicates that the Palaeocene sequence is composed of a shale unit overlain by a carbonate unit. The shale unit contains a rich assemblage of planktic foraminifera indicating Early Palaeocene age (Danian Stage), which is equivalent to the planktic foraminiferal zones P1 and P2. The overlying carbonate unit is Late Palaeocene in age (Selandian-Thanetian) based on the occurrence of several planktic foraminiferal species of the planktic foraminiferal zones P3-P5. The recovery of few species of larger benthic foraminifers from this carbonate unit provides an additional evidence that it was deposited during the Late Palaeocene, corresponding to the shallow benthic foraminiferal biozones SBZ3-SBZ6, which correspond to the (SelandianThanetian) stages. The Early Eocene sequence is mainly barren anhydrites and dolomites with rare badly preserved nummulitids in the Ypresian. The Middle Eocene (Lutetian-Bartonian) limestones contain a nummulitic assemblage with variable species, including Nummulites gizehensis/Nummulites lyelli group, which represent the SBZ14-SBZ16 in the Lutetian and the SBZ17-SBZ18 in the Bartonian. The Late Eocene interval is dated on the presence of few reticulate medium-sized nummulitic species, including Nummulites fabianii, and assigned to the SBZ19. The lowermost part of the Oligocene sequence is attributed to the SBZ21 (Rupelian) based onthe occurrence of Nummulites vascus and Operculina complanata in the limestones. This is overlain by the SBZ22 (Chattian), as indicated by the last occurrence of Nummulites vascus and the first appearance of Borelis melo melo and Amphistegina sp. The uppermost deposits of the studied successions, which are mainly sandstones with hardly any fossils, belong to the Miocene