A stratigraphic review of the Eocene to Miocene rock units in the al Jabal al Akhdar, NE Libya

This paper presents a revision of the Eocene to Miocene rock units of al Jabal al Akhdar (northeast Libya), based on the study of several surface sections in the vicinity of Benghazi and on earlier studies. The gradual disappearance of deep water marine fauna during the Early Eocene (Apollonia Formation) combined with gradual appearances of large-sized nummulitids and coarsening upwards of allochems during the Middle Eocene (Darnah Formation) indicate a shallowing-up trend, which continued to the end of the Miocene. Upper Eocene deposits are missing in the Benghazi area. The Al Bayda Formation (Oligocene) rests disconformably on the Middle Eocene Darnah Formation. The lower part of the Shahhat Marl Member (lower member of the Al Bayda Formation) is detrital and contains reworked Eocene Nummulites together with in situ Early Oligocene N. fichteli and N. vascus. The Algal Limestone (upper member of the Al Bayda Formation) represents Wilson's facies SMF 4, 5 and 6. Cyclicity in this member is notable and it appears to be associated with the regressive and transgressive global fourth-order Cycles TA4.3 to TA4.4. The lower part of the Al Abraq Formation is attributed to the transgressive global fourth-order Cycle TA4.5 and the upper part to Cycle TB1.1. The lower and middle parts of the Al Faidiyah Formation are attributed to the Miocene transgressive Cycles TB1.4 and TB1.5, with the upper part a result of sea level lowering related to Cycle TB2.1. Wilson's facies SMF 7 and SMF 8 typify this formation. The presence of Borelis melo melo indicates that the Benghazi Formation is Middle Miocene in age. It is attributed to Wilson's facies SMF 7 and to the sea level lowering, which corresponds to Cycle TB2.6. The youngest studied rock unit is the Wadi Al Qattarah Formation (Late Miocene) which consists of oolitic packstone and grainstone in the lower part, representing restricted platform conditions and is overlain by evaporites indicating restricted lagoon-salina conditions. © 2008 Elsevier Ltd. All rights reserved.