Stratigraphy and paleoenvironment of the Lower-Middle Eocene succession in the Darnah area, northeast Libya

Abstract

The stratigraphy and paleoenvironment of the Lower-Middle Eocene Apollonia Formation exposed at the northeastern and southern parts of Darnah city, northeast Libya, was studied in detail by means of foraminifera, where rich benthic and planktonic foraminiferal assemblages were recorded. Fifty-seven planktonic foraminiferal species and subspecies belonging to nineteen genera and seven families were identified and seventy-five benthic species and subspecies belonging to thirty-five genera and twenty-three families. The stratigraphic distribution of the recorded fauna in three selected surface sections enabled us to subdivide the studied succession into six planktonic and two benthic zones covering a time interval ranging from the Early to Middle Eocene. The planktonic zones were arranged from base to top as follows: Morozovella edgari, Morozovella subbotinae, Morozovella aragonensis, Acarinina pentacamerata (Early Eocene), Acarinina bullborooki and Globigerinatheka subconglobata subconglobata (Middle Eocene). The benthic zones are represented by the Anomalinoides trinitatensis (Early Eocene) and Bulimina jacksonensis (Middle Eocene). The established zones were discussed and correlated with the international standard zones and with those from neighbouring North Africa and Middle East countries. The Lower/Middle Eocene (Ypresian/Lutetian) boundary was discussed based on the zonal boundaries. The statistical analysis of the identified foraminiferal assemblages for each sample as well as the lithologic characteristics of the Apollonia Formation indicated marine middle to outer neritic setting. The high ratio of the calcareous foraminiferal assemblages and the moderate epifaunal/infaunal ratio reflect deposition in an environment of high calcium carbonate, normal salinity and low to moderate oxygenation levels.