High resolution sequence stratigraphy of the Middle–Late Triassic Al Aziziyah formation, northwest Libya

This study offers the first integration of facies distribution, isotope and sequence stratigraphy studies of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation at its exposure at the Jifarah Basin of northwest Libya. Eight sections were measured along a depositional dip cross-section of the Al Aziziyah Formation. The Al Aziziyah Formation is a 2^nd-order sequence, consisting of mid-ramp and outer ramp carbonate facies, with inner ramp facies restricted to the southernmost sections. The inner ramp peritidal facies indicate arid depositional system characterized by mudcracks, evaporite nodules and abundant cryptalgalaminites. Ramp crest shoals were predominantly peloidal and oolitic packstone-grainstone. However, mid-ramp facies show low to high-density bioturbation. Outer ramp is thin-medium hummocky cross-stratified beds, and interbedded shale. Changes from fine sandstone and red clay to carbonate mark the transition from the underlying Kurrush Formation to the Al Aziziyah Formation. In the most updip location, the transition from the Al Aziziyah Formation to the overlying Abu Shaybah Formation is an iron-rich, phosphatic surface. Seven sequences (S1-S7) within the Ghryan Dome section were identified based on facies stacking patterns, field observations and carbon stable isotope profiles. North of the Ghryan Dome section, there are three mainly subtidal sequences (S8[sbnd]S10) that may not correlate to the south. Higher-order (4th-5th) parasequences are present in the Al Aziziyah Formation, but correlating these parasequences between sections is difficult due to internal erosional discontinuities or autocyclicity.