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Ooids occur in many different environments in the Persian Gulf; blackened relict ooids are common at depths of 100 m in the center of the basin while others have been transported to desert environments up to 40 km from the shore. Most Holocene ooids occur in coastal areas in the S parts of the Persian Gulf in which they appear to be forming in a variety of settings. The most spectacular accumulations constitute tidal deltas associated with coastal barrier system in E Abu Dhabi. Other agitated environments include tidal bars situated in wide channels between islands (Yas and Bahrain) and the adjacent Arabian shoreline, and on open tidal flats and beaches in exposed embayments (Sabkha Matti). Although most ooids are forming in these agitated environments, significant quantities are forming within lagoons (Khor Odaid and Jebel Dhanna), and on the SE lee coast of Qatar Peninsula (Umm Said).

Bored surfaces in Middle Jurassic limestones in northeastern France indicate syn-sedimentary lithification. The sedimentary structures and textures, and age relationships between the bored carbonates and the argillaceous sediments above them suggest that the lithification has occurred in both submarine and intertidal environments. The diagenetic fabrics which have resulted from this early marine lithification include three types of calcite druse, echinoderm overgrowths, and microcrystalline cements. Most of these cements are comparable with those forming today in inter-and subtidal environments of the Persian Gulf.The localization of bored surfaces ("hard grounds") at the tops of regressive carbonate sequences is interpreted as being the result of slow carbonate sedimentation and lithification of the Jurassic sea-floor prior to the onset of argillaceous colder, or deeper-water sedimentation.Present address : Laboratoire de Micropaleontologie, Faculte des Sciences, 9, Quai Saint Bernard, Paris. Sedimentology, 12 (1 969) 205-230Sedimentology, 12 (1969) 205-230

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