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common intercalations of dolomitized oolitic and
intraclastic grainstone layers, suggesting deposition
close to fair weather wave base (proximal inner-shelf
lagoon); (4) stromatolitic and thrombolitic dolostone
(10-150 cm thick) containing isolated to laterally-
linked columnar and domal stromatolite and/or throm-
bolite that show an upward decrease in relief (upper
subtidal to lower intertidal); (5) stromatolites (up to
1-2 m thick) as planar tan- to buff-colored crinkly to
wavy laminites overlain by gray to black planar or dis-
crete to partially-linked microdigitate forms less than
1 cm wide and less than 10 cm high. This facies con-
tains desiccation cracks, irregular to planar birdseyes,
tepee structures, abundant halite casts and rare gyp-
sum and/or anhydrite pseudomorphs (arid upper inter-
tidal to supratidal).
The erosional surface at the base of asymmetric
depositional cycles become more pronounced towards
the shelf margin, suggesting prolonged exposure of the
proximal 'shoal-complex'. The 'shoal complex' periti-
dal deposits overlie the back reef grainstone and stro-
matolite reef facies of the platform margin as a result
of basinward progradation forming the highstand pack-
ages of long-term progradational sequences. Abundant
halite casts and tepee structures and rare gypsum and
anhydrite pseudomorphs in the shelf facies (Grotzinger
1985,
1986a,
b
) suggest that, contrary to Hoffman
(
1975
), arid conditions prevailed during deposition of
the Rocknest Formation.
will be described. In the Tuyeh section, member 2 is
100 m thick and its lower part comprises two deposi-
tional sequences built mainly by peritidal facies. The
lower sequence comprises lowstand, transgressive and
highstand systems tracts built by meter-scale shallow-
ing-upward cycles (Fig.
21.26
).
The lowstand systems tract consists of interlayered
light green- to redish brown, laminated argillaceous
dolomudstone/dolomitic shale capped by reddish
brown, fine- to very fine-grained lithic sandstone
(Figs.
21.19a, b
and
21.26a
). The laminated shale-
carbonate facies contain hopper halite casts
(Fig.
21.19c
) and has no subaerial exposure features.
This facies association is interpreted as a coastal salina
pond deposit. It resembles the carbonate-shale cycles
described by Spencer and Demicco (
1993
) from the
Middle Cambrian passive margin deposits of the
Canadian Rocky Mountains. The brown lithic sand-
stone layers were probably deposited during the
advance of siliciclastics into the coastal plain area
during periods of continental fl ooding. The lower part
of the transgressive systems tract consists of small-
scale shallowing-upward cycles in which interlayered
carbonate and siliciclastic facies just described above
caps wavy- to planar stromatolite facies (Fig.
21.26b
),
which in turn change upward to planar- to wavy- to
domal stromatolite capped by columnar stromatolite
facies (Fig.
21.6e
) recording the most transgressive
facies. Columnar stromatolite bioherms are character-
ized by trapped peloids, ooids and intraclasts and
absence of bioclasts recording deposition in a hyper-
saline and high energy subtidal lagoon to lower inter-
tidal environments similar to Hamelin Pool in Shark
Bay, Western Australia (e.g. Logan, et al.
1970
) . The
highstand systems tract consists of meter-scale periti-
dal cycles. A typical and complete cycle that occurs in
the lower part of the highstand tract (Fig.
21.26c
)
consists of (1) basal individual and compound
columnar stromatolite bioherms subtidal lagoonal
facies (Fig.
21.6e
) grading upward into (2) laterally
linked domal stromatolites lower intertidal facies
(Fig.
21.9b, c
), which in turn grades into (3) wavy to
planar stromatolite upper intertidal facies containing
desiccation cracks, planar fenestrae and calcite
pseudomorphs after gypsum/anhydrite capped by (4)
supratidal facies comprising fenestral and laminated
dolomudstone with gypsum/anhydrite casts. The cycle
is interpreted to have formed by progradation of an
extensive tidal fl at over a high energy lagoon covered
21.7.2 Middle Cambrian Tidalites
in Northern Iran
The Middle and Upper Cambrian was a time of exten-
sive shallow marine carbonate ramp deposition in Iran.
The ramp covered the length of the northern Alborz
Mountains in northern Iran and the Persian Gulf in
southwest Iran (Fig.
21.25
) in the north-northeast fac-
ing Proto-Paleotethys passive margin of northern
Gondwana (Y. Lasemi
2001
), a width of several thou-
sands of kilometers at the time of deposition. In the
Alborz Mountains, the Middle- to Upper Cambrian
deposits includes member 1 carbonates, member 2
mixed carbonate-siliciclastics and member 3 carbon-
ates of the Mila Formation (Stocklin et al.
1964
) . In
this summary, the tidal deposits of the lower part of
member 2 in the Tuyeh section (location 1 in Fig.
21.25
)
of the eastern Alborz Mountains (Amin-Rasouli
1999
)
