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the tidal fl at is bordered to the south by a gently dip-
ping intertidal shoreface. The thickness of Holocene
sediments is typically ~2 m beneath this tidal fl at
(thinning landward) but exceeds 3 m close to the
channel, suggesting that the prevailing geomorphic
pattern is strongly infl uenced by the antecedent topog-
raphy ( Berkeley and Rankey, in review ) .
In the near-absence of channels and associated geo-
morphic features such as levees and ponds, most of this
system is characterized by a supratidal plain dipping
towards the nearshore marine environments (Fig. 19.11b ,
right side). Supratidal areas include extremely subtle
topographic relief (centimeters across the kilometer-
wide tidal fl ats), and are sparsely vegetated with scat-
tered grasses and black mangroves. The infrequent
fl ooding imparts strong evaporative and freshwater
infl uences on surface sediments, and a thin (~1 cm) but
continuous indurated surface with scattered intraclast
debris is present in many areas. Downdip (i.e. south-
ward) from this supratidal zone in the upper intertidal
zone, the sediment surface is colonized by thin (~1 cm),
smooth Scytonema mats, which pass downdip into
thicker (5-10 cm) 'pincushions' upper intertidal zone
with black mangroves. Further towards the coast, around
mean tide level, red mangroves colonize a narrow belt,
and low intertidal to shallowest subtidal areas are non-
vegetated except for localized occurrences of the non-
calcifying alga Batophora and scattered seagrass.
The shoreline delineating the tidal fl ats is notably
irregular, and includes numerous intertidal to supratidal
extensions into the nearshore shallow subtidal areas
(Fig. 19.11 ). The absence of beach ridges suggests that
shoreward-directed wave and tide energy is not appre-
ciable. The irregular shoreline and subtle (~10 cm)
relief may refl ect locally variable rates of sediment
accumulation, perhaps related to patterns of mangrove
colonization.
Adjacent to the single well-developed tidal chan-
nel, a number of intensely burrowed lower intertidal
to subtidal ponds have become partially enclosed by
the development of mangrove-colonized intertidal
bars (Fig. 19.11c ). These features occur on a broad
meander bend where subtle levees with only a few
centimeters of relief have accreted to mean high water.
The outer channel bank is steeper, and the presence of
slabs of thin, indurated crust suggests erosion and
exhumation of previously buried lithifi ed horizons,
like those present in adjacent supratidal areas.
Unambiguous evidence for marked channel migration
is absent in core, however ( Berkeley and Rankey , in
review).
19.4
Arid Tidal Flats of the Arabian Gulf
Sabkhas (arid tidal fl ats) can be found around much of the
western and southern Arabian Gulf (e.g., Purser 1973 ) .
Some of the best studied and most illustrative examples
occur in the United Arab Emirates (UAE; the “Trucial
Coast” of older literature) and on the eastern fl ank of the
Qatar peninsula (Fig. 19.12 ) (Evans et al. 1969 ; Kendall
and Skipwith 1969 ; Purser and Evans 1973 ; Shinn 1973a,
b , 1983a , 2010 in press, Alsharhan and Kendall 2003 ) .
Due to the low precipitation (several cm/year), these sab-
khas include important sedimentologic contrasts with the
humid Bahamian examples. Like the Bahamas, subtidal,
intertidal and supratidal zones include pronounced sedi-
mentologic differentiation; nonetheless, the nature and
distribution of sediments and structures are quite distinct
from those in comparable zones in the Bahamas, and vary
even in different parts of the Gulf.
19.4.1 Eastern Qatar - Zonation,
Subenvironments, and
Geomorphology
The nation of Qatar occupies a club-shaped, north-
south trending peninsula that protrudes into the Arabian
Gulf. On the peninsula's eastern coastline, several
areas include illustrative peritidal geomorphic patterns
(Figs. 19.12 and 19.13 ).
On the northeast coast of Qatar near Khor (Fig. 19.13a,
b ; Shinn 1973a, b ; 2010 ) , a carbonate-dominated shore-
line has prograded up to 5 km from low-lying, highly
irregular outcrops of Tertiary dolomite.
Geomorphic processes here are strongly infl uenced
by the shoreline orientation, which is roughly parallel
to the northwesterly shamal winds. This setting creates
a strong longshore drift from north to south, resulting
in beaches with hook-shaped spits at their southern
end (Figs. 19.13c , d and 19.14 ). These beach-spit
complexes are up to 12 km long and 50-100 m wide
and are comprised of cross-bedded, coarse, bioclastic
grainstone (Fig. 19.14e, f ) with admixed quartz sand
supplied by eolian dunes.
Subtidal sediments include soft, muddy, grey,
reduced, peloidal sediments, which occur immediately
 
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