The Arab-D is the lowermost and thickest of the four members (Arab-A, B, C and D, in descending order) of the Arab Formation, a Kimmeridgian (Upper Jurassic) carbonate–evaporite succession of the Arabian Platform. It is best developed in eastern Saudi Arabia, and extends into Qatar, Bahrain, the UAE and offshore Persian Gulf, where it passes laterally into equivalent units.
Lithology and setting: The member consists of a lower carbonate unit — ooidal, peloidal and skeletal (stromatoporoid–coral–Cladocoropsis) grainstones and packstones, variably dolomitized, grading down into muddier wackestones that merge with the underlying Jubaila Formation. It is capped by the Arab-D Anhydrite, a bedded evaporite seal. Deposition took place on a broad, low-gradient, arid carbonate ramp, with shoal and lagoonal facies giving way upward to restricted, hypersaline sabkha conditions.
