Structural geology of South Hadhramaut area Yemen Republic
The northern margin of the Gulf of Aden has a long history of extension from the Cambrian to the present. The dominant structures are related to Oligo-Miocene rifting in the early stages of development of the Gulf of Aden and they overprint Palaeozoic and Mesozoic structures. An area of 170 km by 50 km was mapped at scale of 1:50,000. Landsat images of the whole area, at 1:50,000 and 1:100,000 and air photographs of part of the area were used as base maps. The resulting maps are the first detailed geological maps to be made for this area and are a major outcome of this research. Precambrian basement which was affected by the oldest stage of extension is overlain by a sedimentary cover sequence from upper Cretaceous through the Tertiary in age. The lower part of this sequence represents the Mesozoic post-rift succession deposited after the second period of extension recorded in this margin. Oligo-Miocene extension has resulted in a highly dissected rift shoulder in which the horizontal cover sequence at an elevation of 1500m to 2500m on the plateau is brought down in a series of tilted fault blocks to sea level at the Gulf coast. The massive, nodular Palaeocene limestone of the Umm er Radhuma Formation forms steep inaccessible fault scarps throughout the area. The faults vary in size from major ones which have strike lengths in excess of 50 km and throws over 1000 m to those that are too small to be recorded on the maps. By measuring the geometry of bedding in the rollover anticlines in the hanging walls of selected faults, the trajectories of the faults at depths were computed. These show that the major faults extend steeply down into metamorphic basement. Major faults with kilometric throws must lie off-shore or, less likely, are buried beneath the syn- and post-rift sediments of the coastal plain.