Abstract:
The objective of the present study is the geochemical assessment of the Bir
Tlacsin Formation at Ghat area, SW Libya. This assessment includes the depositional
environment, paleo-oxygenation, paleoclimate, paleosalinity, provenance, tectonic
setting, organic matter richness, kerogen type and thermal maturity. The field trips
included five surface sections for the formation (Wadi Maghidat, Wadi Tashat, Wadi
Anlakm, Wadi Iggiten, and Wadi Awzarq). This formation consists of sandstone and
shale units. The sandstones are mainly greywackes. The observed clay minerals in the
studied shales are smectite, kaolinite, gibbsite and chlorite. These minerals are the main
carrier of TOC. The Th/Cr, Th/Sc and Th/Co ratios and the provenance discrimination
diagrams indicated that the felsic (granitic) rocks found in the Air Mountains, central
Niger, may be the possible source of the Bir Tlacsin Formation. Based on the ICV
values, the shales are thermally immature whereas the sandstones are thermally
submature to mature. Moreover, the organic geochemical data showed that the organic
matter are thermally immature. The organic matter are essentially of marine origin. The
Zr/Hf, Hf/Ta, Zr/Ta and B/Ga ratios indicated that the Bir Tlacsin Formation was
deposited in a high salinity marine environment. Based on the trace element, Pr/Ph, Pr/n-
C17 and Ph/n-C18 ratios the anoxic conditions were prevalent during deposition. The
paleoclimate prevailing in the source area was almost semi-arid to semi-humid. The
tectonic environment is essentially continental (active continental margin (C) and
passive continental margin (D)). Generally, the shales are good source rocks. The
discrimination diagrams showed that kerogen type II is the basic type in the shale
samples. The hydrocarbons are mainly migrated (nonindigenous).
