Basin Evolution and Tectonostratigraphy of the Late Jurassic Succession, Southern Iraq

Abstract

This study includes the stratigraphic development of the Late Jurassic succession in eight boreholes namely, Si-1, Sal-1, Sa-1, Dn-1, Ki-1, R-172, WQ-15, and KSK -1, within the Mesopotamian Zone. The present study is concluded that the current area represents as part of the northern Arabian plate that was subjected to severe structural deformations prior to the beginning of the Late Jurassic sedimentation, which led to the formation of a vast depression (half graben) that formed a starved basin. This graben was created because of rift-related tectonism called extensional tectonic phase in the latest Middle Jurassic period, which led to the accumulation of high organic matter and formed the source rock (Naokelekan Formation) in the middle part of the graben during their highest and settings. Then this phase was followed by the occupation of the sedimentations (evaporates) in the center of the studied basin during the lowest conditions of the (Gotnia Formation) in the southern Iraq, Kuwait, and southwest Iran. During the highest and system tract after transgressive stage of the Sargelu Formation, the horst surrounding the graben, represents carbonate platforms, which consist of coral structures deposition that follow by Ooids deposits (non-skeletal) and then covered by evaporates sabkha type sediment (cap rock), this succession of sediments called the Najmah Formation. The lowstands stage conditions which are underlying by the sequence boundary type-I, which overlie the Najmah Formation and has been penetrated by Si-1, Sal-1, Sa-1 and Dn-1 wells in the southwestern of Iraq, the sequence boundary considered to be the time equivalent of the Gotnia Formation. The system of the north Arabian plate (Iraq, Kuwait) characterized by an extensional tectonic setting that formed a graben surrounded by shallow water carbonate (horst), while a relatively stable tectonic system predominant at the south-west of the Arabian plate due to its proximity to the Arabian shield, which led to the formation of a wide and flat carbonate platform (Najmah Formation) were covered by Sabkha evaporates.