Mixed siliciclastic–carbonate sedimentary deposits are challenging to interpret due to intermixing of depositional processes and changes in the basin dynamics. The Eocene Musawa Formation outcropping in the Eastern Oman Mountains provides an opportunity to study the sedimentary processes of siliciclastic deltaic sediments deposited over a regional carbonate platform. The Musawa Formation was deposited in structurally constrained Abat Basin formed due to transtensional deformation along Ja’alan and Qalhat faults. These bounding faults provided enormous amount of sediments in a laterally restricted basin undergoing strong tectonic-related subsidence and were fed by a basin axis parallel drainage system. The lithofacies assemblage represents fluvial-dominated deltaic sediments that accumulated as a local siliciclastic feature in a carbonate-dominated subtropical environment. The Musawa Formation consists of four major lithofacies associations: conglomerate, sandstone, siltstone/clay/coal, and carbonate. The coarse-grained lithofacies associations of conglomerate and sandstone were deposited by distributary channels and reworked by shoreface processes, whereas the coastal processes in delta-plain setting deposited siltstone, clay, and coal as overbank fines. The carbonate lithofacies association was deposited in open marine conditions during transgressive events.