Morphotectonic development of Mesozoic carbonates and evaporites of Ath-Thumamah depression in central Arabia

Abstract

The Ath-Thumamah depression exists 20 km north of Riyadh, Saudi Arabia within the Arabian Platform’s interior Homocline, and covers an area of about 50 × 20 km2. This study examines whether the Ath-Thumamah depression has evolved tectonically by extensional faulting event or it is a subsidence-induced depression. The study depends on field-based work, with complementary analysis and interpretations of landsat images and digital elevation maps. The upper Jurassic calcarenite Arab Formation is a regional oil reservoir in Saudi Arabia, and is overlain and sealed by the Hit Anhydrite Formation. The Arab Formation is part of Shaqra Group, and is exposed in the study area and affected by interstratal karstification at the Ath-Thumamah depression. The Arab Formation is overlain by Cretaceous Thamamah Group, which subsequently subsided and collapsed due to dissolution of the Hit Formation. Dissolution and collapse features include basin-and-dome landforms, dissolution breccias, sinkholes and deep canyons. The interstratal features and landforms dominate the Shaqra and Thamamah groups and are limited to the Ath-Thumamah depression. Ath-Thumamah depression is interpreted as a keystone graben, superimposed on a regional open fold, known in this study as Banban anticline. The development of the keystone graben accommodated the deposition of Neogene Sha’al Formation and Quaternary Eolian sand dunes. Karstification features and landforms are developed during the pluvial phases of the Mid Pleistocene time and modified the graben into interstratal karsts depression. Therefore, the Ath-Thumamah depression had developed tectonically and modified by geomorphic processes.