THE INTERIOR RIFTS OF THE YEMEN - ANALYSIS OF BASIN STRUCTURE AND STRATIGRAPHY IN A REGIONAL PLATE TECTONIC CONTEXT

The full extent of Mesozoic rift basins within interior Yemen has only recently been established. This work presents a detailed documentatio n of the stratigraphy, structure and basin development of the Marib-Sh abwa and Sirr-Sayun basins, and the Jeza Trough. Yemen is located at t he south-western margin of the Arabian Plate, which for most of its ea rly geological history formed part of the northern passive margin of G ondwanaland. Mesozoic break up of the super-continent was associated w ith major rifting in the Late Jurassic (main phase) and Early Cretaceo us. Orientation of the rift basins reflects an inheritance from deep-s eated Precambrian structural trends which cross the Arabian Plate. The resultant structure of basement highs, tilted fault blocks, marginal terraces and central graben highs is illustrated in a series of detail ed cross-sections. A comprehensive stratigraphic framework has also be en established for the Jurassic and Cretaceous basin-fill, enabling th ickness and facies variations to be analysed. This reveals a clear shi ft in the main period of fault-related, high sediment accumulation rat es, both within and across the three interior basins of Yemen. In the western Marib-Shabwa Basin, the fill is dominantly Late Jurassic, whil st the eastern Shabwa Basin and Sirr-Sayun Basin exhibit a progressive ly increased, and younger, Early Cretaceous fill. The main period of f ault-related sedimentation in the most easterly basin, the Jeza Trough , is wholly Cretaceous. Plate tectonic reconstructions of the area for this period have documented the separation and subsequent north-eastw ard movement of the Indian Plate, away from Africa-Arabia. We believe this may have been the causal mechanism in the progressive eastward mi gration of rift activity in the Yemen.