First record of shark microremains from the Lower Khartam Member, Khuff Formation: an Upper Permian origin of the genus Lissodus, or a new placement of the Permo/Triassic boundary in Saudi Arabia?

Abstract

Shark fossil microremains belonging to the genus Lissodus are recovered for the first time from the Lower Khartam Member of the Khuff Formation in central Saudi Arabia. Previously published research assigned the Lower Khartam Member to the Upper Permian, implying that this is the oldest known record of the genus Lissodus. On the other hand, the stratigraphic occurrence of the recovered Lissodus lies slightly below the previously defined Permian/Triassic boundary in Saudi Arabia. Because Lissodus specimens are common from the Lower Triassic to the Upper Cretaceous, they may provide paleontological evidence for a revised placement of the Permian/Triassic boundary in Saudi Arabia. The Permian/Triassic boundary has been formerly placed at the contact between the Lower and Upper Khartam members of the Khuff Formation in central Saudi Arabia. Earlier studies relied on sequence stratigraphy and geochemistry as tools for identifying the Permian/Triassic boundary. This resulted in placing the boundary at different stratigraphic levels, reflecting the ongoing uncertainty about its actual position. In this study, two scenarios are discussed arguing either for a revised placement of the Permian/Triassic boundary, or a possible Late Permian origin for the genus Lissodus on the Gondwanan continent.