Geology Reference
In-Depth Information
Hill include: (1) fenestral lime mudstone with calcite
pseudomorphs after anhydrite and/or thickly inter-
laminated peloidal grainstone to mudstone with irreg-
ular to tabular fenestrae, root casts, and desiccation
cracks (supratidal) (Figs.
21.15a, b
,
21.17a
and
21.18a, b
); (2) millimeter-thick interlamination of
micrite-rich and fi ne sand- to silt-sized bioclast/pel-
oid-rich carbonates or fl at- to wavy stromatolites com-
monly containing dolomudstone, molds of fi lamentous
cyanobacteria, desiccation cracks and calcite pseudo-
morphs after lenticular gypsum (upper intertidal)
(Figs.
21.3a, c
,
21.9d
, and
21.10c-e
); and (3) biotur-
bated lime mudstone to packstone commonly contain-
ing peloids, oncoids and bioclasts (Fig.
21.5d
) of a
restricted fauna that commonly includes gastropods,
ostracods, and benthic foraminifera (lower intertidal/
subtidal lagoon). The Cave Hill Member represents an
unconformity bounded depositional sequence (3rd-
order cycle) on which are superimposed numerous
small-scale fourth- to fi fth-order cycles (Fig.
21.28
).
In the Cave Hill sequence, peritidal small-scale cycles
comprise the bulk of the highstand systems tract and
display aggradational and progradational stacking
patterns (Fig.
21.28
). The absence of peritidal depos-
its in the transgressive tract may be the consequence
of a rather fast sea level rise during the onset of depo-
sition of the Cave Hill Member.
A similar carbonate tidal deposit occurs in the lower
part of the Middle Mississippian St. Louis Limestone
of the Illinois Basin and its equivalent in the Michigan
Basin. In southwestern Illinois, a peritidal succession
with a basal unconformable boundary is present in the
lower part of the lower St. Louis Limestone (Z. Lasemi
and Norby
1999
). This interval includes cyclic biotur-
bated lime mudstone to intraclast/bioclast peloid and/
or oncoid wackestone-grainstone containing a low-
diversity fauna (subtidal) capped by wavy- to planar
stromatolites or laminated peloid mudstone-grainstone
(lower intertidal) overlain by mud-cracked peloidal
dolomudstone/lime mudstone (Fig.
21.17c
) with fenes-
tral fabric, calcite pseudomorphs after gypsum or dis-
solution collapse breccia (supratidal). The breccia beds
change laterally to gypsum and anhydrite beds in the
subsurface, thus, they are related to collapse of the
overlying limestone layers after dissolution of gypsum
and anhydrite beds (Saxby and Lamar
1957
) . The per-
itidal facies grades upward to deeper marine facies and
is interpreted here as the lowstand systems tract of a
depositional sequence. This interval is correlated with
the lower part of the Bayport Formation in the Michigan
Basin, which includes: (1) millimeter to centimeter
thick beds of interlayered quartz sandstone and dolo-
mudstone/lime mudstone with calcite pseudomorphs
after gypsum, lamination, desiccation cracks, rain
drop impressions, birdseyes, microbial lamination and
heterolithic stratifi cation including wavy, fl aser and
lenticular bedding (Figs.
21.11
and
21.12a
) recording
deposition in an arid tidal fl at adjacent to an aeolian
sand fl at; (2) dark gray bioturbated ostracod mudstone
and/or microbial laminites (Fig.
21.16a
) interpreted as
an intertidal pond facies; and (3) sandy peloid,
restricted-fauna bioclast mudstone to packstone
lagoonal facies (Y. Lasemi
1986
). In the St. Louis and
Bayport Formations, the peritidal deposits occur in the
lower part of the sequence and are here interpreted to
have been deposited during lowstand and transgressive
sea level rise.
21.7.5 Triassic Tidalites of Northern
and Central Iran
During the Triassic, thick shallow marine carbonates
were deposited under arid conditions on carbonate
ramps that covered the northern Cimmerian Plate of
central and northern Iran (Paleo-Tethys margin) and
the northeast Gondwanan continent (Neo-Tethys mar-
gin) of southwest Iran (Fig.
21.25
). The Elika Formation
(up to 1000 m thick) in northern Iran is the uppermost
unit of a thick platform carbonate succession related to
the north-facing Paleo-Tethys passive margin that
existed from Devonian through early Late Triassic
times (Y. Lasemi
2001
) . This summary discusses the
lower and middle Elika (Lower-Middle Triassic) in the
central Alborz Mountains of northern Iran (Paleotethys
passive margin) and the Sorkh Shale Formation (the
lower Elika equivalent) in the Tabas failed rift basin of
east central Iran (Fig.
21.25
).
21.7.5.1 Lower Elika Member
The unconformity bounded lower Elika is up to 200 m
thick and consists of thin to thick-bedded limestone
with thin shale intercalations. This summary concen-
trates on the lower Elika of the Veresk section and the
middle Elika of the type locality (Fig.
21.25
, locali-
ties 2 and 3, respectively) and is adopted from Jahani
(
2000
). The lower Elika member consists of subtidal
open marine and grainstone shoal facies in the lower
part changing upward to lagoonal and intertidal facies
(Fig.
21.29
). Peritidal facies comprise the middle and
