| Author(s) | Ahmad A. AI-Aswad*and Omar A. AI-Harbi** |
| Affiliation | Department of Geology, College of Science, P.D. Box 2455, Riyadh 11451, Saudi Arabia Natural Resources and Environnwnt Research Institute, King Abdulaziz Cityfor Science and Technology, P.D. Box 6086, Riyadh 11442, Saudi Arabia |
| Title | Stratigraphy, Provenance and Depositional Evolution of the Minjur Sandstone (Upper Triassic) in Saudi Arabia |
| Source | Journal of King Saud University. Science. Volume 12, No 1. (2000/1420) |
| Abstract | The Upper Triassic Minjur Sandstone is weU-exposed in continuous outcrops that extend for more than 1000 km across central Saudi Arabia. The formation is composed dominantly of cross-bedded sandstone with minor amounts of shale and rare conglomerate. The sandstones are mineralogically mature quartzarenites composed largely of monocrystalline non-undulalory fluartz. Modal composition, quartz polycrystallinity, undulosity and heavy minerals were used to deduce the provenance of the Minjur Sandstone. This integrated approach suggests that the Minjur Sandstone largely was derived from older mature sandstone deposits with minor contributions from igneous and metamorphic rocks. The Cambro-Ordovician Saq Sandstone is the most probable precursor of most of the. Minjur sediments. The Upper Triassic sedimentary rocks in central Arabia represent a major regressive sequence deposited during a time of prolonged eustatic sea-level fall. The Minjur siliciclastic sediments were deposited in a broad complex of paleoenvironments, ranging from alluvial plain in the west, through coastal paleoenvironments to shelf carbonates further east. The distribution of these Upper Triassic facies and their related paleoenvironrnents was controlled by interplay between climate and tectonics. The paleoclimate was generally becoming more humid over the Arabian Peninsula in the late Triassic, which intensified chemical weathering in the source area, and led to increased precipitation that activated sluggish streams thus contributing to the enlargement of their alluvial plains. Tectonic movements associated with the opening of the neo- Tethys and the closure of the paleo- Tethys contributed locally to the lowering of the sea level in the area. Structural elements prevailing in the area also controlled the sedimentation pattern by constructing barriers to the advancing Tethys Sea in some areas acting as sediment traps in others or by elevating source areas to the west of the subsiding basin. |
