Geology Reference
In-Depth Information
Fig. 19.16
Character of the coastal system, Abu Dhabi, United
Arab Emirates, southern Arabian Gulf (Fig.
19.12
). In this area,
the shoreline faces into the dominant winds. (
a
) Khor al Bazam
area, south of Al Qanatir Island (labeled “AQ”). In this region,
a series of older beach ridges (
black arrows
; Kirkham
1997
)
are bordered oceanward by a series of microbial-mat facies
belts (“MM”) that generally parallel the shoreline (Kendall
and Skipwith
1968
) . (
b
) Area to the east. A broad intertidal
to supratidal mangrove fl at (
reddish
color), penetrated by
tidal creeks
the open ocean by closely spaced “T”-shaped islands
(Fig.
19.16
). The islands have one long axis parallel to
the NE-SW oriented shoreline, with an elongate per-
pendicular stem extending leeward (NW-SE). Beaches
on the exposed, seaward sides of these islands can have
beach ridge dunes up to 5 m high, refl ecting the high-
energy conditions. These supratidal ridges are com-
posed primarily of medium to coarse skeletal sand,
including abundant gastropods, and unlike beach sand
of Bahamian tidal fl ats, these sediments are commonly
reworked into eolian dunes. The type of sand (skeletal,
oolitic) is closely related to the nearshore sediment.
In the subtidal realm, large oolitic tidal deltas are
found seaward of tidal inlets between islands in this
area (Fig.
19.16
); reefs also may be present in areas in
front of the islands protected from lagoonal waters
extruded through tidal passes (Alsharhan and Kendall
2003
). Extensive early cementation, creating hard-
grounds up to 30 cm thick, occurs in areas oceanward
of the islands. In many places, the elongate leeward
(landward) stems of islands are fl anked by broad inter-
tidal fl ats which gradually slope into the protected
lagoon (Fig.
19.16b
). On these fl ats the lower intertidal
mangrove swamp includes abundant black mangrove,
Avicennia sp.
, which grows in areas penetrated by
small tidal channels and fl ooded daily. These man-
groves may facilitate the formation of small levees,
and these areas tend to accumulate oxidized muddy
sediments that are extensively burrowed by crabs.
Microbial mats are not as expansive here as in other
supratidal areas; instead, the lateral transition from the
lagoon to the sabkha is relatively abrupt.
Areas west of the Zubaiya peninsula are downwind of
the Qatar peninsula, and are not exposed to the full wave
