Sedimentology of mixed siliciclastic-carbonate system in a structurally constrained Paleogene basin: Eocene Musawa Formation in Eastern Oman Mountains

The Middle Eocene sedimentary succession in Abat Basin contains a thick mixed siliciclastic and carbonate sequence belonging to the upper member of the Musawa Formation. Over 300 m thick deltaic sediments of the Bartonian to Priabonian upper member of the Musawa Formation show two main facies successions over ten km distance, grading from a proximal delta-plain to a distal delta-front succession. Four major lithofacies associations based on their depositional significance are identified in the basin, namely the conglomerate, sandstone, mudstone, and carbonate. Each of these lithofacies associations is further divided into several individual lithofacies based on their depositional characteristics. The lithofacies association assemblage represents fluvially-dominated deltaic sediments that accumulated as a local siliciclastic feature in a carbonate dominated tropical environment. The conglomerate and sandstone lithofacies associations were deposited by channels and shoreface processes, whereas coastal processes in delta-plain setting deposited mudstone lithofacies association (including coal). The carbonate lithofacies association was deposited in an open marine shelf conditions during transgressive events associated with highstands of sea level and delta-lobe switching. The occurrence of thick siliciclastic sediments is interpreted as the result of activation of the North Ja'alan Fault resulting in a transtensional basin during the Middle to Late Eocene.