Sirhan–Turayf and Widyan basins’ boundary and Upper Cretaceous lateral changes in northern Saudi Arabia

This study is conducted on the Northern Borders Province, northernmost Saudi Arabia, mapping a newly identified Wadi Al Khirr transtensional fault zone, based on detailed fieldwork, image interpretation as well as GIS work. The Wadi Al-Khirr fault zone extends from west of Al Uwayqilah to Zahwah. Remote sensing satellite data indicate that it can be projected further to the south toward the central Arabian Shield. About 100 km to the east of the newly proposed fault zone, late Cretaceous Linah Formation is changing its eastern lithofacies within the Widyan basin. The changes in lithofacies represent the results of tense diagenetic alteration (many phases of dolomitization/de-dolomitization), accompanied by silicification and carbonate leaching of the carbonate rocks. This western (Mediterranean) and eastern (Arabian Gulf) lithofacies appear to be laterally equivalent in biostratigraphy as it is evidently having Loftusia sp. in both sides. The lithofacies changes occur 100 km to the east of the Wadi Al Khirr fault zone; therefore, it is likely postdating the Upper Cretaceous sequences and may not be associated tectonically with the east to west lithofacies. The Sirhan–Turayf and Widyan basins’ boundary is found in this study to have complicated tectonic setting. Wadi Al Khirr fault zone to the east, and the Makkah-Madinah-Nafud with newly interpreted Sakaka lineaments to the west bound the Ha’il arch, separating the two basins. Moreover, the Ha’il arch is cross-cut and deformed by Ar’Ar arch in the upper northern part of the study area and by reactivation of Najd Faults to the south.