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.