Sedimentological and sequence-stratigraphic analyses of the Tithonian Hith Anhydrite Formation in the Dahal Hit outcrop, Saudi Arabia

The Dahal Hit cavern in Central Saudi Arabia is the only locality where the Tithonian Hith Anhydrite Formation is exposed in the Middle East. In 2010, a 28.5-m interval in the 90-m-thick Hith Formation was logged and described in the cavern as part of a study to evaluate its sedimentological and sequence-stratigraphic architecture and to identify potential high-permeability layers within the seal of the world’s most prolific petroleum system. Seven facies types were interpreted as reflecting sabkha (subaerial) or salina (subaqueous) settings, and their vertical stacking patterns revealed that the logged interval consists of three transgressive–regressive cycles and part of a fourth cycle. The cavern was revisited in 2016 but only to find that the water level had risen by about 50 m rendering further geological studies impossible. The higher level of the water suggests that the cavern was flooded by the flow in the subsurface of treated sewage water released into a former quarry. The quarry is situated about 10 km southeast of the cavern, and the storage of water in it started in 2008. The flow pathways to the Dahal Hit cavern are apparently well-connected karsts, caverns, and high-permeability flow zones present in dolomite layers.