Geology Reference
In-Depth Information
Fig. 9.35
Features of typical stratigraphic units compromising
Tonglu tidal-flat successions, upper Wenchang Formation of
Late Ordovician. The Tonglu tidal-flat successions consist of a
complete cycle (A) from the subtidal facies to the upper inter-
tidal facies and a half cycle (B) with upper part of intertidal
facies associations.
PCB
, low-angle planar cross-bedding;
LB
,
lenticular bedding;
WB
, wavy bedding;
FB
, flaser bedding; Anjie
Fm, Anjie Formation of Early Silurian (After Fan et al.
2004b
)
9.7.2.2 Islay (Late Proterozoic)
The Lower Fine-grained Quartzite of Middle Dalradian
(Late Proterozoic) age in Islay, Scotland, consists of
massive-bedded, cross-stratified, and rippled ortho-
quartzites (Facies 1), and siltstone and mudstone
(Facies 2). The two facies are organized into a sharp-
based, fining-upward succession with basal shallow
subtidal sandstones, intertidal sand-flat or sand-bar
sandstone, and high tidal-flat mudstones (Klein
1970
).
The succession is highly identical to that of back-bar-
rier tidal-flat deposition (Klein
1985
; Dalrymple
1992
),
except the general devoid of tidal-channel deposits.
Comparison study prefers the modern analogue in the
Wash of Eastern England with few presence of inter-
tidal channels (Klein
1970
), falling into the divisions
of open-coast tidal flats.
subjected to sufficient storm-induced wave activity
(Chaudhuri and Howard
1985
). Such facies interpreta-
tion sought no acceptable modern analogue at that time
(Chaudhuri and Howard
1985
), but is now comparable
with the facies model of open-coast intertidal deposits
building over the distributary-mouth or estuarine-
channel bars (Fig.
9.32b
).
9.7.2.4 Hazel Patch (Late Carboniferous)
The Hazel Patch sandstone of the Pennsylvanian age
(Late Carboniferous) in eastern Kentucky (USA) has
been highlighted for developing cyclic tidal rhythmites
registering three orders of tidal cyclicities, including
diurnal inequality, neap-spring cycle, and monthly
tidal cycle (Greb and Archer
1995
). Actually, cyclic
tidal rhythmites are spatially limited in the lower part
of a single major channel-filled succession. Within the
channel fill, cyclic rhythmites grade upward into amal-
gamated rhythmites. The broad flats outside of the
major channel are exclusively dominated by noncyclic
rhythmites, containing small rhythmic successions
similar to those of storm-generated successions on
modern open-coast tidal flats (Figs.
9.27
and
9.28
).
The Hazel Patch sandstone is generally a fining-upward
succession, consisting of the subtidal sand-bar deposits
and the intertidal broad sand-flat deposits (both containing
9.7.2.3 Ramgundam (Middle Proterozoic)
The Ramgundam Sandstone of Middle Proterozoic
age is well exposed along the Godavari Valley of south-
central India (Chaudhuri and Howard
1985
). It is com-
posed of lens-shaped bodies of arkosic sandstone and
interbedded sandstone and shale. The fining-upward
succession devoid of tidal-channel deposits presum-
ably represents a transgressive intertidal depositional
succession building over linear-bar shoals frequently
