Tidal flat rocks and sediments along the eastern coast of the United Arab Emirates

The geomorphologic and petrographic characteristics of the calcareous hard rocks in the intertidal and supratidal zones of the eastern coast of the Un ited Arab Emirates, where it faces the Gulf of Oman, were investigated The tidal zone can be broadly classified into two major physiographic provinces . A northern province that has a rather steep profile and a tidal net that is very narrow and is characterized by lithoclasts of gravelly sand sedimen ts. It is formed of beachrocks, well-developed coastal terraces and cliffs and is bounded landward by mountains composed mainly of peridotite and gabb ros. The southern province tidal fiat is much wider than the north province with a shallow, tide dominated and sheltered coast where sandy bioclasts a ccumulate. The mountains surrounding such areas are located several kilomet ers 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 ge nerally sloping seaward. These rocks are partly covered by beach sand, skel etal debris, algae and other rock fragments encrusted 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 f iat benches that vary in their geomorphologic pattern and three well-develo ped terraces are recognized. Based on the composition of framework grains, beachrocks can be grouped into two types: lithic and bioclastic. The lithoc lasts are mainly composed of peridotite, gabbros, pyroxenes, calcareous roc k fragments and washed sediments derived from wadi-fill and dust storms. Th e bioclastic sediments are chiefly fragments of corals, foraminifera, pelec ypods, gastropods, crabs, echnoids and algae. The beachrock cement is mainl y formed by aragonite, micrite and coarsely crystalline calcite with a subo rdinate amount of dolomite, Precipitation of aragonite appears to be mainly controlled by the micrite substrate and at least three successive stages o f cement fill are observed.