The Upper Jurassic sediments, Marib-Shabwa Basin, Yemen: Lithofacies aspects and sequence stratigraphic analysis

Abstract

The present study is devoted to understanding the evolution of the Upper Jurassic Sab'atayn Formation in the Marib-Shabwa Basin, Yemen, through a sequence stratigraphic analysis based on integrating datasets of sedimentology, seismic sections, and well logs. The Sab'atayn Formation (Tithonian age) is represented by a series of clastic and evaporites that were deposited under fluvio-deltaic to prodeltaic settings. It is divided into four members including Yah (at the base), upwards to Seen, Alif, and Safir at the top. Two third-order depositional sequences were determined for the Tithonian succession which were separated by three sequence boundaries. These sequences were classified into their systems tracts signifying several sedimentation patterns of progradational, aggradational, and retrogradational parasequence sets. The first depositional sequence corresponds to the early-middle Tithonian Yah and Seen units that can be classified into lowstand, transgressive, and highstand systems tracts. The second sequence comprises the late Tithonian Alif unit that can be subdivided into transgressive and highstand systems tracts. The sandy deposits of the Alif Member (highstand deposits) represent the most productive hydrocarbon reservoir in the basin. The Upper Jurassic sediments in the study area were resulted from a combination of eustatic and tectonic effects.