MICROFACIES ANALYSIS AND DEPOSITIONAL ENVIRONMENTS OF THE SHUQRA FORMATION AT JABAL ALMAHDAD, MASWAR DISTRICT, YEMEN REPUBLIC

The Shuqra Formation is one of four prominent formations of the Amran Group (Middle Jurassic-Lowermost Cretaceous) of the Yemen Republic. This formation overlies the stratified sandstone beds of the Kuhlan Formation. The study section (Jabal Al-Mahdad) is located at the Maswar District, 40km. west of Amran town. The stratigraphic sequence in Jabal Al-Mahdad is characterized by basement complex comprising Akbra Shale, Kuhlan Formation, Amran Group and Tawilah Group.
Fifty-four samples were collected and examined in detail to determine the microfacies and then to interpret the depositional environment of the Shuqra Formation in the study area. Four major microfacies are distinguished from those samples. These microfacies include: mudstone, wackestone,packstone and grainstone. Wackestone is the dominant one and is pelletical and fossiliferous (foraminiferal, ostracodal and algal) subfacies while packstone is pelletical, oolitic and fossiliferrous (crinoidial) subfacies. The grainstone microfacies is distinguished to fossiliferous and pellitical.
The identified microfacies indicated that the Shuqra Formation in this area was deposited in a shallow marine environment within restricted platform, open platform and winnowed platform. The water energy level has changed from agitated (during oolitic subfacies time) to moderate (during the wackestone time) and quite (during mudstone time).