Lithofacies Associations and Depositional System of the Muti Formation, Oman Mountains

The Upper Cretaceous Muti Formation of the Aruma Group was the first unit deposited in the Oman foreland basin in the Oman Mountains. The Oman foreland basin is a major hydrocarbon-producing basin with great future exploration potential. A few studies were published in the early 1990; however, no detailed work on the sediments of the Muti Formation has been done since then. The closure and compression of the southeast margin of the Tethys Ocean during the Upper Cretaceous resulted in thrusting and obduction events and erosion of the Arabian platform, known as the Wasia-Aruma break. The Semail Ophiolite and Hawasina Complex were obducted over the eastern margin in northeast Oman, and the platform drowned, flexed, and faulted, resulting in the foreland basin development. The Muti Formation is well exposed around the Jabal Akhdar Dome, and a total of 14 outcrop sections are measured and described to identify the lithofacies associations and depositional setting of the formation. These lithofacies are correlated across various sections to help understand their distribution and depositional environments. The Muti Formation thickness ranges from 13.4 to 179 m and comprises nine lithofacies. These lithofacies are grouped into four lithofacies associations, namely wackestone to mudstone, monomictic conglomerate, laminated claystone, and ferruginous clays. Based on these results, the formation is lithologically subdivided into a lower and upper parts. A diverse fossil assemblage was observed within the wackestone to mudstone lithofacies, including ammonites, bryozoans, bivalves, brachiopods, and gastropods. The Muti Formation records the transition from a passive margin to a foreland basin deposited in a shallow marine environment. The lower part is dominated by wackestone to mudstone lithofacies association rich in fossils accumulated in the middle carbonate shelf. The upper part of the formation is composed of siliciclastic lithofacies deposited on the outer shelf under low energy conditions. The findings of this study shed light on the lithofacies distribution and depositional system of the Muti Formation across the foreland basin.