Sequence Stratigraphy and Depositional History of the Eocene-Miocene Carbonates and Evaporites in the Subsurface of the Northern Mesopotamian Basin, Northeast Iraq

George Grabowski¹*, Chengjie Liu¹, and Augustus O. Wilson^2
1ExxonMobil, USA
²Consultant, USA
*[email protected]

Our integrated study of plankton biostratigraphy, petrography, Sr87/Sr86 age dating, and well-log correlation for IPC wells is leading to a new, unified sequence-stratigraphic framework and a revised depositional history for the Middle Eocene to Lower Miocene in northeast Iraq. Subaerial-exposure and flooding surfaces define progradational shelf-margin sequences in the Upper-Middle Eocene limestones of the Avanah and Pila Spi formations. The shelf margins become steeper towards the top, reflecting increasing accommodation in the basin. Time-equivalent basinal carbonates of the Jaddala Formation have flooding surfaces and interpreted hardground surfaces that define parasequences that are uniform in thickness. Two sets of progradational shelfal to shelf-margin limestones of the Oligocene Kirkuk Group pass laterally into basinal globigerinid limestones. Tops of shelfal sequences were subaerially exposed and eroded, and the prograding shelf margins again become steeper towards the top. The Ibrahim Formation is time-equivalent to the Tarjil Formation and part of the Palani Formation and in places to the upper part of the Jaddala. The Anah and Azkand formations are approximately time-equivalent to the Bajawan and Baba formations. The Serikagni Formation consists of many parasequences of basinal carbonates defined by regional flooding surfaces and is Chattian. It is overlain by the Euphrates Formation, a shelfal deposit with multiple higher-order cycles bounded by subaerial-exposure surfaces and anhydrites. The overlying Dhiban Formation consists of basin-filling anhydrite and argillaceous-limestone beds. The anhydrites are dated to 21.0–22.2 Ma, placing the Euphrates and Dhiban formations within the late-Aquitanian lowstand. The overlying Jeribe Formation consists of shelfal limestones of the Late-Aquitanian HST and the basal-Burdigalian sequence, which are separated by a regional subaerial-exposure surface. Shoaling-upward parasequences stack aggradationally and lap onto the margins of the basin.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain