Campanian–Maastrichtian unconformities and rudist diagenesis, Aruma Formation, central Saudi Arabia

Abstract

The Upper Cretaceous Aruma Formation is widely distributed in central Saudi Arabia and consists of three members, from base to top, the Khanasir Limestone Member, the Hajajah Limestone Member, and the Lina Shale Member. It disconfomably overlies the Cenomanian Wasia Formation (middle Turonian, the “Wasia-Aruma break”). Two unconformities were recorded within and at the top of the Aruma Formation: (a) “the lower Campanian unconformity” between the Khanasir Limestone Member and the Hajajah Limestone Member and (b) “the pre-Cenozoic unconformity” between the Lina Shale Member and the Paleogene Umm er Radhuma Formation. The comparison between these unconformities and those recorded on the Arabian Plate was emphasized. A lenticular rudist biostrome in the uppermost part of the Khanasir Limestone Member consists mainly of the radiolitids and sparse canaliculated rudists in life position. However, rudists are entirely fragmented in the lower limestone and are very rare in the upper limestone of the Hajajah Limestone Member. Loose right valves of radiolitids from the Campanian Khanasir Member have underwent diagenetic alterations, such as fragmentation and compaction, micritization, bioerosion, and micritic calcite cement, which indicates marine diagenetic stage, while very limited silicification, dolomitization, and dissolution suggest the meteoric diagenetic environments with arid climates. Isopachus and equant calcite cement and neomorphism may be showed the fresh pharetic zone related with subaerial unconformities.