Geology Reference
In-Depth Information
Fig. 21.3
(
a
-
c
) Laminated tidal fl at deposits and (
d)
intertidal
and lagoonal deposits: (
a
) Thin section photograph showing
interlamination of mud and fi ne sand- to silt-size carbonate. Note
cement-fi lled desiccation crack in the
lower left
. Thickness varia-
tion of the laminae may refl ect daily variation of tidal range
(neap-spring cycles); Cave Hill Member of the Mississippian
Kinkaid Formation in the Buncombe Quarry, southern Illinois.
(
b
) Mud-cracked laminated tidal fl at facies in the Middle
Devonian Vernon Fork Member of the Jeffersonville Limestone,
southwest Indiana (Photo courtesy of Dr. B.D. Keith, Indiana
geological Survey). (
c
) Thin section photograph of interlami-
nated planar- to wavy stromatolite (
darker laminae
) and dolo-
mudstone. The graded intraclastic upper lamina was formed by a
storm tide; Cave Hill Member of the Mississippian Kinkaid
Formation in the Kinkaid Creek section, southern Illinois. (
d
)
Field photograph of a succession composed of
bluish gray
sub-
tidal limestone overlain by
light grayish brown
to tan intertidal
dolomudstone. The contact between the subtidal and intertidal
facies appears to be sharp; Lower Triassic lower member of the
Elika Formation, Alborz Mountains, northern Iran
21.5.2 Intertidal Belt
peloids and intraclasts (Fig.
21.8a
) and may grade
landward into a narrow belt of lower energy intertidal
(foreshore) facies. The tidal channel deposits at the
platform margin may consist of laminated horizontal
strata and/or cross-bedded (sometimes bidirectional)
gravel- and sand-size intraclastic ooid/bioclast grain-
stones (Fig.
21.8b
) and/or columnar microbialites.
The intertidal belt is fl ooded and exposed once or twice
daily and consists of various facies with diagnostic
features. The arid upper intertidal sediment commonly
consists of mud-cracked laminated facies deposited by
tidal currents (Fig.
21.3a, b
) and/or planar to wavy
