Foraminiferal palaeoenvironmental constraints in the Sirt Shale (late Campanian-early Maastrichtian) transgressive succession of the Hameimat Basin) northern Libya

Abstract

The Sirt Shale consists of a transgressive succession ranging in age from late Campanian to early Maastrichtian. The investigated area includes the deeper section of the Hameimat Trough (eastern Sirt Basin) flanked by higher relief to the north and east. Planktonic and benthonic foraminifera are used as a tool in determining biostratigraphy and palaeoecologic setting. Spatial and stratigraphic distributions suggest a depth stratification of the planktonic taxa, with intermediate (epi- to mesopelagic) water exchange with the main Sirt Basin from the latest Campanian. Limits on biostratigraphic resolution are indicated by the late introduction into the Hameimat Basin of the single-keeled globotroncanids. Dominance of low-oxygen tolerant taxa characterizes the benthonic foraminiferal faunal composition. A striking reduction in species diversity at the top of the succession in the deep basin has been interpreted as the establishment of a mid-water oxygen-minimum zone.