Abstract
Rocks of the Amran Group in the Sana'a region of Yemen disconformably overlie the Kohlan Formation and unconformably underlie the Tawilah Group. Sea-level rises have produced landward migration of facies belts and the development of deeper water facies over shallow ones. The geometry of the depositional environments identified has enabled the passage of relatively short-lived transgressive-regressive cycles of sedimentation to be recognized. Three facies associations are introduced: (1) Carbonate platform facies, (2) Carbonate-marl alternation facies, and (3) Shallow water coral and stromatoporoid build-up facies. These facies are widely distributed and the whole sequence reflects deposition on a broad platform upon which shoals separated platform carbonates from basin sedimentation and an open marine environment. The repetition and interfingering of both fining- and shallowing-upward cycles within the study areas suggest that deposition occurred within the same basin with slightly different conditions in different places. The main factors controlling their deposition are sea-level changes and tectonics.
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