The underlying sediment of Bubyan is comprised of distinctly laminated and thinly bedded layers of Aeolian silts and sandy to silty cohesive clay. The upper part is dominated by gypsum precipitation. In summer, increased evaporate growth induces lateral and upward buckling of the slightly hardened, salt encrusted surface. The sediment of Bubyan cannot be classified as truly coastal or continental sabkha because it has features of both. The ground-water table is more than two meters deep. In summer, the surface is kept alternately damp and dry by the high evening humidity and extreme mid-day heat combined with a hot, dry wind. In winter, the surface and near surface are moist to water-logged in times of rainstorms.

The interior sabkha of Bubyan depends largely on rainfall, which settles and slowly permeates about one meter. The fine-grained, thinly bedded terrigenous deposits of the island, produced by deltaic sedimentation, differ from the classical carbonate sequence of the coastal sabkha of the southern Gulf in terms of sabkha dynamics and host sediments, water chemistry, and diagenesis. The habitat of deposition on the island was greatly influenced by several major depositional cycles of fluviatile, estuarine, marine, and to a lesser degree, Aeolian sedimentation. Interpretation of the stratigraphy shows Holocene transgression (brackish followed by marine) and regression (marine followed by brackish) sequences.

There have been extreme changes in sea level in the Gulf after late Pleistocene glaciations. During the final episode of glacial maximum in late Wisconsin Glaciation (between 30,000 and 17,000 years ago) sea level fell rapidly and reached its lowest level of -120 meters, about 16,000 years ago. This resulted in the shoreline of Shatt Al-Arab estuary and the Gulf being withdrawn 1,000 kilometers toward Hormuz at the entrance of the Gulf of Oman.

Fluviatile erosion and Aeolian sedimentation operated freely within the drained dry Gulf until Holocene marine transgression flooded the Gulf basin once more. During the early Holocene sea level rise, river estuary, or freshwater lakes and marshes, were partially filled with fluvial-deltaic sediments as rivers draining this area responded to the changes in base level. In the Gulf, temporary coastline stabilization occurred at about -10 meters around 7,000 years ago. After a short pause, the Holocene sea continued rising rapidly, pushing north toward the Mesopotamian plain.

The shoreline approached the present position of the Shatt Al-Arab delta and the south end of Bubyan Island possibly as long ago as 6,500 to 6,000 years ago.

During this period, the area which was to become Bubyan was submerged and became the site of deposition of mixed lacustrine and brackish water. Between 6,000 and 5,500 years ago there was a rapid marine advance across the former marsh flats and lakes of southern Mesopotamia, which marked the start of deposition of a marine sequence of silts and sands. The shoreline attained its most landward limit just south of Amara probably 5,000 years ago, then began to with draw, with progradation continuing to this day. By about 4,500 and 4,000 years ago, Bubyan began to emerge, first as a mud shoal, then growing by rapid channel in filling and intertidal estuarine sedimentation as the sea receded.

Concurrent with the drop in sea level, the rivers or their major distributaries changed course, and their concentrated flows entrenched khors around the emergent Bubyan.

Failaka Island

Failaka Island is surrounded by several morpho - sedimentary units. Extensive, soft tidal flats and rocky beaches abound; these are composed of medium to coarse sand.
Prior to the Gulf War, the island was inhabited by 5,000 people with remarkable range of socio - economic activities . Most of these people were resettled in and around Kuwait city following the hostilities.