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Stable Isotope Chemostratigraphy of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation, NW Libya

Mohamed S. Moustafa
Department of Geology and Geophysics, Texas A&M University, College Station, Tx, United States, [email protected]

The Middle to Late Triassic (Ladinian-Carnian) Al Aziziyah Formation was deposited on a gently sloping carbonate ramp within the Jifarah Basin Northwest Libya. This unit consists of mixed carbonate and siliciclastic rocks of gray limestone, dolomite and dolomitic limestone interbedded with shale. This unit is a potential oil reservoir especially toward the northern part of the basin. Two sections (the Ghryan Dome and Kaf Bates sections) were sampled and analyzed for stable isotope chemostratigraphy to determine the age model of the formation and to correlate between sections.

The δ 13C values range from +3.9 to -7.8 ‰ and the δ 18O values range from +3.4 to -7.4 ‰.The enrichment of δ 13C is most likely due to a low diagenesis effect from meteoric fresh water and to the withdrawal of C12 from the ocean during the deposition of shale and organic- rich sediment. However, depletion of δ 13C values is likely related to input of CO2 from atmosphere and oxidization of organic matter. Enrichment of δ 18O is related to low meteoric fresh water input and early lithification of carbonate sediments with slight or no interaction with diagenitic waters. However, depletion of δ 18O is related to a diagenetic effect during the deposition of the Al Aziziyah Formation. This study presents the first δ 13C and δ 18O curves from whole rock of the Al Aziziyah Formation. Those curves show similar patterns with the global Middle- Late Triassic δ 13C and δ 18O curves from brachiopods and whole rock data.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013