Salt domes and their control on basin margin sedimentation: a case study from the Tihama Plain, Yemen

This chapter examines the Pliocene and Quaternary post-rift sediments overlying, and deformed by, the intrusion of salt diapirs on the coastal plain of Yemen in the south-eastern Red Sea. The coastal plain region has been dominated by siliciclastic deposits (Al Milh Sandstone) derived from erosion of the Yemen rift shoulder escarpment and deposited in a range of fluvial, lacustrine, aeolian and shallow-marine environments. These have accumulated on and around, and have been intruded by, the Salif Evaporite which forms a 3 km high salt wall that outcrops at the Salif salt mine. The Pliocene to Holocene Kamaran Limestone is deposited on and seaward of the Salif salt wall and thickens offshore through Kamaran Island to offshore wells. The salt wall is considered to have acted as a barrier to sediment transport from the rift margin resulting in ponding of siliciclastic sediments on the coastal plain and offshore carbonates.

The upper surface of the Salif salt diapir underwent differential sea-floor dissolution as the salt uplifted into the shallow-marine environment. Less soluble rafts of gypsum and dolomite formed upstanding ridges surrounded by locally derived conglomerates. Coral patch reefs and carbonate sands and gravels accumulated within a few metres of the dissolved upper surface to the salt. Analysis of the coral fauna indicates that it comprises a number of taxa tolerant of increased levels of turbidity but only a few taxa are tolerant of increased salinity. A thin cover of sediment and strongly stratified water column is thought to explain the unusual occurrence of a fully marine fauna close to the dissolved salt.

Carbon and strontium isotopic dating of the limestones indicates older (Pliocene-Pleistocene) tilted beds on the flanks of the diapir and younger (Holocene) reef limestones on top of the diapir today occurring at an altitude of 16–20 m above sea level. These relationships reflect those seen on a seismic section through the diapir, indicating that the rise of the salt is punctuated by periods of subsidence.