LITHOSTRATIGRAPHY AND ENVIRONMENT OF DEPOSITION OF THE MIDDLE CAMBRIAN SEDIMENTARY ROCKS IN NORTHWESTERN SAUDI ARABIA

Lithostratigraphic field investigations and interpretations of the Middle Cambrian sedimentary rock units, southern of the Tabuk basin northwestern Saudi Arabia, provide insights into depositional environments and stratigraphic framework in Paleozoic succession in the Arabian platform. Moreover, it provides new record of an extensive marine influence of the Middle Cambrian transgression. The lithologic studies were carried out on four measured sections in the new formation, which is named Shigri formation and located in Haqal, Al Bada, Al Ula and Jibal Al Misma in northwestern Saudi Arabia. This formation varies from 25-80 m in thickness and contains a light brown bioturbated medium to fine-grained sandstone with vertical Skolithos trace fossils burrows that are horizontal to wavy bedding, sigmoidal cross bedding and sandy cross-bedded conglomerate capped by very fine grained and silty sandstone. The formation overlies unconformably the Early Cambrian fluvial Ash Shiq sandstone Formation of the lower part of the Tayma Group and underlying the Middle Cambrian fluvial Al Ula sandstone Formation. This formation crops out in a curved belt from the Saudi-Jordan border to the southeastern corner of the Jibal Al Misma quadrangle, west of Hail in Saudi Arabia and an equivalent to the Abu Khusheiba sandstone Formation in Jordan. The Shigri formation interpreted as shallow marine environments with continental fluvial influx. The evidence of a shallow transgression marine origin includes vertical Skolithos trace fossils burrows and sigmoidal cross bedding, while the sandy cross-bedded conglomeratic channels indicative of fluvial influence to shallow marine deposits. This study provides insights into the new formation, fluvial-shallow marine sedimentation, and identification criteria for the Middle Cambrian sandstone.