Coastal Alluvial Fans of the Raghama Formation, Northern East Red Sea, Saudi Arabia

Four Miocene outcrops of the Raghama Formation have been investigated for the first time in NW Saudi Arabia to identify facies types, facies associations, and sequence stratigraphy. These sections have been controlled by fans that flow into the sea from higher altitudes. The fans can be divided into alluvial fans and a braided fluvial environment that pass seaward into lagoons and fringing reefs. The continental deposits of the fan are characterized by the fan apex, which passes downslope into alluvial plains. These alluvial deposits are located beside high hinterlands and contain dwindling gravel pavement and local dunes. The transitional zone between the continental and marine deposits comprises mainly erosional beaches and sheet flood sediments. The fan in the marine environment is regulated by longshore drift and wave action. The fringing reef is located offshore from the fan and close to the shore with no lagoons. The fringing reefs are locally affected by the force of the water rushing down the active streams, as indicated by the occurrence of irregularities, remnants, and gravels in the reef cervices. One third-order depositional sequence is well preserved within the studied sections. This sequence is bounded by unconformities and is controlled by the ratio between accommodation and sediment supply (A/S ratio). Variations in the A/S ratio are related to eustatic sea level, climate, and tectonics related to the collision between the Eurasian and Arabian plates, the latter which is responsible for the uplift of the studied areas and the widening of the Red Sea, leading ultimately to subsidence during the Middle Miocene.

Automated summary

The study investigated four Miocene outcrops of the Raghama Formation in NW Saudi Arabia for the first time, identifying facies types, facies associations, and sequence stratigraphy. The sections are controlled by fans flowing into the sea from higher altitudes, transitioning from alluvial fans and braided fluvial environments to lagoons and fringing reefs. The study revealed a well-preserved third-order depositional sequence, with variations in the A/S ratio related to factors such as sea level, climate, and tectonics.