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SURFACE BOCKS
Rocks ranging in age from early Miocene to Kecent are exposed on the surface throughout the State of Kuwait. The very low dips and similarity of lithology make correlation of formations difficult, as marker beds can be traced accurately for only short distances. Along the Jal-Az-Zor escarpment three formations can be recognized, owing to the presence of fossiliferous clays of the Lower Fars Formation which separate the over- lying Dibdibba Formation from the Ghar Formation.
Where the Lower Fars cannot be recognized, no sub- division is possible, and the entire sequence is called the Kuwait Group.Detailed descriptions of the formations follow.

RECENT BEDS (QUATERNARY)Kecent deposits within Kuwait consist of the follow- ing types:Beach deposits are composed of reworked sandstone from the Kuwait Group; these sands may be cemented with calcium carbonate and are current bedded. Some oolitic limestones and shelly limestones also occur. The fossils within these beds have been correlated with present species.Extensive deltaic and tidal mudflats are found in northeastern Kuwait, Bubiyan Island, and along the north shore of Kuwait Bay. These are composed pre- dominantly of plastic clay and silt having a high saline content. The material is considered by the author and others to have been deposited by the Tigris-Euphrates Kiver system.Deposits formed in inland drainage basins are usually very fine silt and clay with a variable percentage of sand and a very high salt content.Windblown sand is common.

DIBDIBBA FORMATION (MIOCENE TO PLEISTOCENE)The Dibdibba Formation in Kuwait consists of all beds above the f ossilif erous horizons of the Lower Fars Formation except for Recent deposits. The formation is composed of sands and gravels with minor clay and gypsiferous sandy clay beds. The beds show poor to medium stratification and in places the sands are cemented by calcium carbonate and gypsum. The upper part of the formation consists of coarse gravels de- posited in sheets and trains. These gravels are composed of metamorphic and igneous rock debris. J. D. Moody (unpub. data, 1947) has recognized two dis- tinct groups of pebbles on the basis of shape analysis. One group has a high average roundness whereas the other has medium to low average roundness. The first group is composed of quartz and metamorphic rocks with lesser amounts of silicic igneous rocks and is con- sidered by Moody to have been derived from Najd and the Hijaz. The second group is composed of various types of silicic and mafic volcanic rocks and is thought by Moody to have been derived from the lava flows of the Syrian Desert and northern Arabia.These gravels differ widely in size, but a general in- crease in average size is noticeable toward the west. In ravines along the east side of the Wadi al Batin, ellipti- cal boulders, as much as 2 feet in length along the major axis, have been found. No diagnostic fossils have been found in the Dib- dibba Formation. In that the Dibdibba grades down- ward into the Lower Fars Formation of Miocene age, the lower part might be at least this old. If the volcanic rocks found in the gravels in the upper part of the for- mation are derived from the lava flows of northern Arabia, which are reported to be of Pliocene and Pleis- tocene age, these gravels could not have been deposited before the late Pleistocene. For these reasons the Dib- dibba Formation is believed to range in age from Miocene through Pleistocene.

LOWER FARS FORMATION (LOWER TO MIDDLE MIOCENE)The only outcrop that is definitely Lower Fars For- mation occurs in the Jal-Az-Zor escarpment in the Bahrah area as a 125-foot unit and is comparatively distinct from the formations above and below. The lithology as described by Cox and Rhoades (unpub. data, 1935) consists of alternating red and yellow sand-stones, red and green clays, and various intermediate clayey sandstones and silty clays.Fossils are moderately common, but individual fossil beds cannot be traced laterally for more than 1 or 2 miles. The most persistent fossil is a small lamelli- branch which, according to Cox and Rhoades, is similar to the Clausinellas of the Lower and Middle Fars beds of Iran. The lamellibranch is found alone or associ- ated with Ostrea vestita, Ostrea latimarginata, Dendri- tina cf. D. rangii, Turritella sp., Lucina sp., and Balanus sp. The presence of the above species and lateral corre- lation with the Lower Fars of Iran places the Lower Fars of Kuwait in the lower to middle Miocene.

GHAR FORMATION (OI.IGOCENE AN1> LOWER MIOCENE)At the foot of the Jal-Az-Zor escarpment the Ghar Formation can be definitely identified owing to the presence of the overlying Lower Fars. In the vicinity of Bahrah approximately 100 feet of section is exposed. The lithology consists of current-bedded coarse-grained to pebbly sandstones which show a nodular sugary- weathering surface. Some of the sandstones are firmly cemented and calcareous, and a few green clay beds are scattered through the section. Information from the Kuwait Oil Co.'s Bahra 1 well shows that the Ghar is 800 feet thick in this area and that it directly overlies the Dammam Formation of Eocene age.No fossils have been identified in the section, but from stratigraphic considerations alone, Owen and Nasr (1958) have assigned the Ghar Formation to the Oligocene and lower Miocene.

KUWAIT GROUP (MIOCENE, FXJOCENE, AND PLEISTOCENE)South of Kuwait Bay where the Lower Fars is absent, no subdivision of the beds above the Dammam Forma- tion can be made, so they are simply called the Kuwait Group. Outcrops in southeast Kuwait consist chiefly of gray to yellow clayey sandstones with some pebbly sandstones. No more than 30 feet of continuous section is exposed at any one place and consequently lateral correlations are not possible.In this area, at Wara and Burgan, there are hills which are capped by hard brown-weathering siliceous sandstone and chert.
At Gurain hill, which is near the Kuwait boundary with the Neutral Zone, a thin bed of hard white cherty limestone approximately 2 feet thick occurs at the top. According to Cox and Rhoades (unpub. data, 1935), this limestone is due to chemical precipitation, and its exact position in the sequence is doubtful.

SUBSURFACE ROCKS
A brief description of the lithology of the subsurface formations which have been penetrated by drilling is as follows.EOCENE FORMATIONSThe formations identified as being of Eocene age range in thickness from 2,500 feet in southeast Kuwait to 3.200 feet in west Kuwait and range in age from Pale- ocene to middle Eocene. The sequence is composed pre- dominantly of limestone except for an evaporite sequence (Rus Formation) of middle Eocene age. The contact with the Cretaceous is conformable.

CRETACEOUS FORMATIONSThe Cretaceous ranges in thickness from 6,000 feet in southeast Kuwait to 10,000 feet in northwest Kuwait. The lithology consists predominantly of limestone and subordinate shale and two major sandstone formations which are present in the Lower and middle Cretaceous. These are the Zubair Formation of Early Cretaceous age which is approximately 1,300 feet thick, and the Burgan Formation of middle Cretaceous age which is approxi- mately 1,100 feet thick.PRE-CRETACEOUS FORMATION'SAlthough the top of the Jurassic has not been ac- curately determined, it is at present (1964) chosen as the top of the first anhydrite bed below rocks of Early Cretaceous age. This anhydrite is believed to be equiv- alent to the Hith Anhydrite of Saudi Arabia. Very little information is available about formations older than Cretaceous, as only two wells in Kuwait have penetrated formations below the Hith Anhydrite.

A deep test in the Burgan field was drilled to 13,853 feet and at this depth was in rocks believed to be of Triassic age. At present, 4,500 feet of rock in this well is be- lieved to be of Jurassic age. Of this 4,500 feet, the uppermost 1,500-foot section is evaporite beds and the remaining 3,000-foot section is limestone and some marl, shale, and thin anhydrite. The beds assigned to the Triassic consist of 627 feet of clay, marl, shale, and sandstone. Mutriba 2 in northwest Kuwait was drilled 1,715 feet below the Hith Formation. The upper 1,610 feet is evaporite beds and the lower 105 feet is dense limestone.

STRUCTURE
Regionally, Kuwait lies at the edge of the Arabian foreland on the southwest flank of the Persian Gulf geo- syncline. The regional dip is to the northeast at about 9 feet per mile. This regular-dip surface is interrupted by the Kuwait arch and by other major structures,
KUWAITF7which are present at Raudhatain, Umm Gudair, and Minagish. These structures are very gentle and no dips over 3° have been identified. Subsurface information indicates that these structures have been growing almost steadily since at least middle Cretaceous times, and pos- sibly they are as old as Late Jurassic. The evidence in- dicates that the growth of the structures is the result of vertical movement rather than horizontal compression, especially in pre-Miocene times, but the exact cause of this movement has not been determined. The exception to the above is the Ahmadi structure, which appears to be the result of horizontal compression in post-Eocene times and is probably related to the Zagros orogeny.