Unconformity and Paleokarst in the Lower Part of the Qamchuqa Formation; An Example from the Arabian Carbonate Platform in the Zagros Belt NE Iraq

Abstract

Northeastern Arabian Plate Margin is now part of the Zagros Collisional belt and extends nearly parallel to the Iraq-Iran border. The margin comprised, during the Early Cretaceous, of the Arabian Carbonate Platform which is poorly explored. This margin consists of thick carbonate succession and separates the Neo-Tethys Ocean (present Sanandaj-Sirjan Zone) from the Arabian Plate interior. The carbonate succession, as the Qamchuqa and Balambo formations, consists of more than 600 m of dolomite and reefal limestone. The present study focused on records and discussions of evidence of unconformity and paleokarst (UaPK) inside the Arabian platform in northeast Iraq. The study recorded this evidence inside the lower part of the Qamchuqa Formation and the pieces of evidence include limestone conglomerate, plaeo-solution cavities, erosional surfaces, widespread coarse and fine grain detrital limestones, hardground, extensive burrows of Thalassiniodes, and mineralization. The solution cavities shaped a complex network, developed inside fine-grain limestone and filled with yellow to brown ooid and detrital limestones. Most of these features are observable over more than 500 km2 in the Sulaymaniyah and traceable inside gorges and valley sides. Toward the north and northeast of the studied area, the unconformity changes to correlative conformity in the Neo-Tethys basin of the studied area where the sediments consist of laminated and graded detrital limestone (packstone-wackstone) and are deposited as a thick succession of calciturbidite that stratigraphically designated as the Balambo Formation. The result of the present study debates the previously claimed unconformities and uncovers many processes and features of the Northeastern Arabian Carbonate Platform Margin. Additionally, it reveals tectonic and paleogeographic settings of the Arabian Plate Margin that have application in searches for oil and better reconsideration of the geologic setting of the Zagros Belt in the future.