Sequence Stratigraphy of the Middle-Late Triassic Al Aziziyah Formation, Jifarah Basin, NW Libya

The Jifarah Basin in northwestern Libya is bounded by the Nafasah uplift to the south and the offshore Sabrath Basin to the north. Core data from several wells drilled in the basin indicate deposition of Paleozoic to Jurassic sediments. The Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation consists of massive grey limestone, dolomite and dolomitic limestone with interbedded shale. This unit is a potential oil reservoir interbedded with good source rocks especially toward the western part of the Sabrath Basin.

The Al Aziziyah Formation in the Jifarah Basin is being studied to better understand it’s distribution of facies and sequence stratigraphy. Eight measured sections (Ghryan Dome, Ras Mazal East, Ras Mazal West, Kurrush Dome, Kaf Bates, Al Aziziyah Town, Ras Lafal and Bu Arghop ) record a depositional dip cross section of the Al Aziziyah Formation within the Jifarah Basin. Detailed stable isotope (C, O) chemostratigraphic studies of the Al Aziziyah sections at Ghryan Dome and Kaf Bates will provide a clearer understanding of the chemical record preserved in this unit.

The Al Aziziyah Formation is predominantly a 2nd-order (10-20 m.y. duration) subtidal carbonate ramp with tidal flats restricted to the southernmost sections. Tidal flats were arid with mudcracks, evaporite nodules and stromatolites. Ramp crest shoals were predominantly pellet packstone-grainstone, whereas subtidal carbonates are thin-medium beds with hummocky cross-stratification, mechanical lamination and low to high density bioturbation. Bed thickness variations may define higher-order sequences, but correlating these sequences between sections is difficult. The homogeneity of meter-scale cycles in the Al Aziziyah Formation subtidal facies suggests these rocks were deposited during a global greenhouse climate mode. The transition from the underlying Kurrush Formation to the Al Aziziyah Formation is marked by a change from fine sand and red clay to carbonate. In the most updip location the transition from the Al Aziziyah Formation to the overlying Abu Shaybah Formation is an iron and phosphatic surface (composite exposure and flooding surface) overlain by a bone bed and fine sand.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California