FACIES DISTRIBUTION, SEQUENCE STRATIGRAPHY, CHEMOSTRATIGRAPHY, AND DIAGENESIS OF THE MIDDLE-LATE TRIASSIC AL AZIZIYAH FORMATION, JIFARAH BASIN, NW LIBYA A Dissertation

Mohamed Salem, Hamadi Moustafa, Ethan Grossman, Yuefeng Sun, Walter Ayers
2015 unpublished
This study presents the depositional facies, sequence stratigraphy, chemostratigraphy and diagenetic evolution of the Middle-Late Triassic Al Aziziyah Formation, Jifarah Basin northwest Libya. Eight measured sections were sampled and analyzed. High-resolution stable carbon isotope data were integrated with an outcrop-based sequence stratigraphic framework, to build the stratigraphic correlation, and to provide better age control of the Al Aziziyah Formation using thin section petrography,
more » ... petrography, cathodoluminescence (CL) microscopy, stable isotope, and trace element analyses. The Al Aziziyah Formation was deposited on a gently sloping carbonate ramp and consists of gray limestone, dolomite, and dolomitic limestone interbedded with rare shale. The Al Aziziyah Formation is predominantly a 2 nd-order sequence (5-20 m.y. duration), with shallow marine sandstone and peritidal carbonate facies restricted to southernmost sections. Seven 3 rd-order sequences were identified (S1-S7) within the type section. North of the Ghryan Dome section are three mainly subtidal sequences (S 8-S 10) that do not correlate to the south. Shallowing upward trends define 4 th-5 th order parasequences, but correlating these parasequences between sections is difficult due to unconformities. The carbon isotope correlation between the Ghryan Dome and Kaf Bates sections indicates five units of δ 13 C depletion and enrichment (sequences 3-7). The enrichment of δ 13 C values in certain intervals most likely reflects local withdrawal of 12 C from the iii ocean due to increased productivity, as indicated by the deposition of organic-rich sediment, and/or whole rock sediment composed of calcite admixed with aragonite. The depletion of δ 13 C is clearly associated with exposure surfaces and with shallow carbonate facies. Heavier δ 18 O values are related to evaporetic enrichment of 18 O, whereas depletion of δ 18 O is related to diagenesis due to freshwater input. Al Aziziyah Formation diagenetic events indicate: 1) initial meteoric and shallow burial; 2) three types of dolomite D 1 , D 2 and D 3 were most likely formed by microbial, seepage reflux and burial processes, respectively; and 3) diagenetic cements cannot be related to the arid, mega-monsoonal climate of the Triassic and most likely formed subsequently in a humid, meteoric setting. iv DEDICATION This dissertation is dedicated to my father and mother for their encouragement, to my wife and children for their support and patience. v ACKNOWLEDGEMENTS
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