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The geomorphologic and petrographiccharacteristicsof the calcareoushard rocks in the intertidal and supratidal zones of the eastern coast of the United Arab Emirates,where it faces the Gulf of Oman, were investigated. The tidal zone can be broadly classifiedinto two major physiographicprovinces. A northernprovince that hasa rather steep profile and a tidal flat that is very narrow and is characterized by lithoclastsof gravelly sand sediments. It is formed of beachrocks, well-developedcoastal terraces and cliffs and is bounded landward by mountainscomposed mainly of peridotite and gabbros. The southem provincetidal flat is much wider thanthe north province with a shallow, tide dominated and sheltered coast where sandy bioclasts accumulate. The mountains surroundingsuch areas are located severalkilometers from the coast and are largely formed by gabbros.Beachrocks are developed as discontinuous beds in narrow belts of pavement, limited essentially to the intertidal zone and with a surface, which is generallysloping seaward. These rocks are partly covered by beach sand, skeletal debris, algae and other rock fragmentsencrusted by living organisms. They rest on dense to friable loose beach sand mainly composed of biogenic fragments strongly bonded by carbonate cements. Tidal terraces are almost flat benches that vary in their geomorphologic pattern and three well-developed terraces are recognized. Based on the composition of framework grains, beachrocks can be grouped into two types: lithic and bioclastic. The lithoclasts are mainly composed of peridotite, gabbros, pyroxenes, calcareous rock fragments and washed sediments derived from wadi-fill and dust storms. The bioclastic sediments are chiefly fragmentsof corals,foraminifera,pelecypods,gastropods,crabs, echnoidsand algae. The beachrockcement is mainly formed by aragonite, micrite and coarsely crystalline calcite with a subordinate amount of dolomite. Precipitation of aragonite appears to be mainly controlled by the micrite substrate and at least three successive stages of cement fill are observed.

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