Miocene benthic foraminifera from the Soluq area, ne Libya: biostratigraphy and environmental significance

Abstract

Six stratigraphic sections along the north-south scarp that traverses the middle of the Soluq area of Libya, about 70 km southeast of Benghazi were studied. Based on their lithofacies and faunal content, two rock units (carbonate and mixed siliciclastic-carbonate) belonging to the Miocene Ar Rajmah Group are reported. The two rock units are separated by a well marked unconformity. The base of the Benghazi Formation has been dated as Lower to Middle Miocene based on the presence of an assemblage of benthic foraminifera. Miogypsinoides complanatus (Schlumberger), Nephrolepidina sp. and Miogypsina cf. globulina (Michelotti) are the main diagnostic taxa in the Aquitanian and Burdigalian. The Middle Miocene interval of Benghazi Formation is ascribed to the Langhian and Serravallian where Operculina complanata (Defrance) and Borelis melo melo (Fichtel and Moll) are the main time-specific diagnostic taxa; the latter taxon occurs also in other coeval deposits of Libya.An Upper Miocene age is attributed to major deposits of the later rock unit. The last occurrence of Amphistegina cf. lessonii d’Orbigny, Heterostegina cf. costata (d’Orbigny) and the associated small benthic foraminifera characterize the contact between the Tortonian and the Messinian deposits of the Wadi al Qattarah Formation.The variation in lithology and fossil assemblages discussed here reflects the variety of environmental settings characterizing the studied Miocene sequence, indicating an overall shallowing-upward trend, from open platform (Benghazi Formation) to restricted platform and restricted lagoon-salina conditions (Wadi al Qattarah Formation).