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Tectonics, basin evolution and evaporites |
1 Research Center for Dams and Water Resources, Mosul University, Mosul, Iraq (e-mail: alialjubory{at}yahoo.com)
2 Applied Geology Department, Tikrit University, Tikrit, Iraq
3 Northern Oil Company, Kirkuk, Iraq
Two depositional basins were present in the Kirkuk Basin of northeastern Iraq during the Burdigalian and Early Langhian ages (Late Lower–Early Middle Miocene) and have been studied at several oilfields. Both basins display shallowing upward sequences composed of carbonate and evaporite sediments. Evaporites form part of the sedimentary sequences that begin with normal open marine and shelf deposits and pass upward into thickly bedded and massive- nodular anhydrite that alternates with thinly bedded limestone (dolomitized with anhydrite nodules), and that is unconformably overlaid by massive bedded lagoonal limestone. The first basin of (Burdigalian age) is represented by the Serikagni, Euphrates and Dhiban formations, whereas the second of Langhian age includes the Jeribi and Fat'ha formations. The early part of the Burdigalian age is characterized by a marine transgression that covered a large part of the region, resulting in a broad spectrum of marine environments ranging from the open marine in the uppermost part of the gentle slope environments, evidenced in the Serikagni Formation, to the shallower environments of fore- and back-shoals of the Euphrates Formation. Regression took place at the end of this period and resulted in the deposition of the Dhiban Anhydrite Formation. The basin of deposition of the Dhiban Formation is an inherited basin from the older Serikagni and Euphrates basins. This is reflected in an inhomogeneous distribution, both of type and thickness, of evaporites. The Early Langhian age of the Kirkuk Basin is also characterized by a shallowing-upward sequence begun by sediments rich in planktonic foraminifera for the lower part of the Jeribe Formation and then shallow water and lagoonal carbonates for the upper part of the Jeribe Formation. The environment passed upwards into the evaporitic sequence of the Fat'ha Formation.
