environment after a relative sea-level drop. The preferred
habitat of most erect, rigid, branching bryozoans is gen-
erally a calm milieu below the storm wave base (e.g.,
Smith
1995
), but with shallowing they may have become
reworked and accumulated in shallower water. The marls
above (A15–19) document a renewed deepening.
Sandstones and coarse-grained conglomerates from
above the marls (A21–23) indicate a relative sea-level
lowstand and mark the beginning of the third sequence.
With ongoing deepening the coarse siliciclastic content
decreases upsection and the lithology shifts into an alter-
nation of silt, silty marls and clays (A24–29). The
associated mollusk fauna (Harzhauser
2004
) and sirenian
bones imply seagrass vegetation in a shallow environment.
A shallow and turbid environment is also reflected by the
Porites-Tarbellastraea assemblage in bed A30. The pre-
vailing platy and branching coral growth forms are inferred
to be adaptations to a high influx of fine siliciclastic
material (Wilson and Lokier
2002
; Rosen et al.
2002
). With
rising relative sea-level the siliciclastic input decreases and
skeletal limestones composed of corallinaceans and larger
foraminifers (A31–32) were formed, which are typical for
the middle ramp. Above follows a unit of bryozoan rich
marl (A33), again suggesting deposition in a relatively
deep environment. Leptoseris-dominated coral build-ups
(A34), which are indicative of low light levels in a deeper
environment (Kahng and Maragos
2006
), mark the maxi-
mum flooding of the third sequence. The upsection
decrease of clay as well as the high proportion of light-
dependent biota (corallinaceans, larger foraminifers, cor-
als) in the carbonatic unit on top of section Zefreh A
document a fall in sea-level. The associated coral fauna is
characterized by Porites with platy growth morphologies,
which typically occur in turbid, low light settings with a
high input of fine siliciclastics (Wilson and Lokier
2002
).
This scenario is supported by the high amount of matrix in
the framing skeletal limestones.
The upper part of Zefreh section (Zefreh B) belongs to a
new sedimentary cycle. Strong siliciclastic influx from the
volcanic arc now prevails while the formation of skeletal
limestones, containing terrigenous clasts and showing a
reddish color, occurs rather sporadically. The strong input
of siliciclastics indicates uplift of the volcanic arc that
superimposed the eustatic sea-level signal. Therefore,
shallow marine conditions of an inner to mid-ramp envi-
ronment continuously prevailed during deposition of the
siliciclastics and limestones above (B4–30). This is sup-
ported by the omnipresence of light-dependent biota and
absence of deeper water faunal elements, such as planktic
foraminifers, abundant erect bryozoans, and Leptoseris
corals. Indicator for a turbid, relatively nutrient-rich envi-
ronment is the monotypic Porites assemblage in beds B15
and B18 (Wilson and Lokier
2002
). The upper part of the
section documents siltation as suggested by the shift from
gray to red silty marls that grade into continental silici-
clastics of the Upper Red Fm. (B28–30). An intercalated
bed of miliolid grainstone (B29) implies a shallow restricted
environment of an inner shelf lagoon (Sen Gupta
1999
).
Depositional environments in the Qom back-arc basin
Qom section
Section Qom includes seven depositional sequences. The
first sequence starts with biolaminites and large scale cross-
bedded, oolithic, skeletal grainstones (2–3, 5–6) of the a-
Member. They are interpreted as subaquatic dunes that
formed in the peritidal and shallow subtidal zone and that
were deposited during a relative sea-level lowstand.
The a-Member deposits are covered by mudstones of the
b-Member, implying a deeper and calm offshore milieu
owing to the occurrence of abundant plankton. However,
the two intercalated packages of cross-bedded grainstones
(8, 10), also interpreted as subaquatic dunes, indicate short
episodes with recurrence of shallow subtidal conditions and
are assumed to represent lowstand deposits of a second and
a third sequence. For the third sequence, the marl succes-
sion of the lower subunit of the c-Member (11), the muddy
substrate, and the abundant occurrence of plankton and
erect branching bryozoans suggest a deeper offshore and
relatively low energy environment that evolved during a
new rise of relative sea-level. Yet the associated larger
foraminifers document deposition to have taken place in
the photic zone even at this stage. The corallinacean-
bryozoan facies of the marl/limestone succession of the
middle subunit (12–29; Fig.
10
d) is indicative for sediment
export from a moderately deep environment during relative
sea-level lowstand of the fourth sequence.
A new drop of relative sea-level is indicated by a bed of
cross-bedded sandstone (31) and furthermore by a general
increase of terrigenous material. A unit of gypsum in the
basal d-Member (33) documents hypersaline conditions
during relative sea-level lowstand, initiating the fifth
sequence. In the Qom section, rippled sandstones and
siltstones on top of the gypsum (34, Fig.
5
d) are indicative
of a very shallow environment. Upsection these sand- and
siltstones are laminated, suggesting an increasing water
depth, and grade into a unit of marls (35–36), for which the
associated fauna implies fully marine conditions. Bryozoan
floatstone interbeds at the base of the marl unit (35) indi-
cate a relatively deep environment, whereas the ooids,
forming a succeeding bed, are interpreted to having been
reworked from a shallow source area.
Thick gypsum deposits (37; Fig.
5
e) reflect a relative
sea-level fall and restriction of the basin during lowstand at
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