Carbon and oxygen isotope variations of the Middle–Late Triassic Al Aziziyah Formation, northwest Libya

• Published in: Journal of African earth sciences (1994) 2016-06, Vol.118, p.149-162
• Main Authors: Moustafa, Mohamed S.H., Pope, Michael C., Grossman, Ethan L., Mriheel, Ibrahim Y.
• Format: Article
• Language: English
• Subjects: Al Aziziyah Formation; Ghryan Dome; Jifarah Basin; Kaf Bates; Libya
• ISSN: 1464-343X; 1879-1956
• DOI: 10.1016/j.jafrearsci.2016.02.011

This study presents the δ13C and δ18O records from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation that were deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya. The Al Aziziyah Formation consists of gray limestone, dolomite, and dolomitic limestone interbedded with shale. The Ghryan Dome and Kaf Bates sections were sampled and analyzed for carbon and oxygen isotope chemostratigraphy to integrate high-resolution carbon isotope data with an outcrop-based stratigraphy, to provide better age control of the Al Aziziyah Formation. This study also discusses the relation between the facies architecture of the Al Aziziyah Formation and the carbon isotope values. Seven stages of relative sea level rise and fall within the Ghryan Dome were identified based on facies stacking patterns, field observations and carbon stable isotopes. The Al Aziziyah Formation δ13C chemostratigraphic curve can be partially correlated with the Triassic global δ13C curve. This correlation indicates that the Al Aziziyah Formation was deposited during the Ladinian and early Carnian. No straight-forward relationship is seen between δ13C and relative sea level probably because local influences complicated systematic environmental and diagenetic isotopic effects associated with sea level change. •This study presents the δ13C and δ18O stratigraphies from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation.•Al Aziziyah Formation was deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya.•The lower portion of the Al Aziziyah δ13C curve correlates with the Tethyan Triassic δ13C curve based on brachiopod shells.•Negative δ13C values are clearly associated with exposure surfaces and with shallow carbonate facies.•More positive δ18O values (up to +0.5‰) are related to evaporatic enrichment of 18O. The depletion of δ18O is related to diagenesis due to freshwater input.