Geology Reference
In-Depth Information
Table 9.4
Comparison of couplet number and thickness on the daily and fortnightly tiles for the field observation on the Nanhui
Mudbank in the Changjiang Delta during the period
May 24 to July 8 in 1999 (A
fter Fan and Li
2002
)
Daily tiles
Fortnightly tiles
Preservation rates (%)
1
3
2
4
2 vs. 1
4 vs. 3
Cumulative thickness of couplets (mm)
303.2
335.4
65.0
92.2
21.4
27.5
Cumulative number of couplets
81
77
16
16
19.8
20.8
Average couplet thickness (mm)
3.7
4.4
4.1
5.8
Sedimentation rate (cm year
-1
)
245.9
272.0
52.7
74.8
Fig. 9.30
Modeling output of the distribution pattern of the preservation potential over the transect DT-DM in Northern Jiangsu
coast for different bed slopes: (
a
) tan E = 0.5 × 10
-3
; (
b
) tan E = 1.0 × 10
-3
(After Gao
2009
)
roughly 96 years, and were on average composed of 32
small successions (Fig.
9.31
). The small succession is
a storm-related thinning- and fining-upward succes-
sion, consisting of a couple of SDLs and MDLs, which
are a group of sand- or mud-dominated layers, respec-
tively, generated by storms or after the storms. Single
small succession generally represents annual cycle of
storm season and non-storm season deposition
(Fig.
9.27
), so only one third of 96-year depositional
intervals contain their own deposits, and the diastems
occupy the other two-third time intervals. Assuming
the even distribution of the diastems, their temporal
distribution is shown in Fig.
9.34a
. Over 1-year inter-
val, the temporal distribution of diastems looks like
that of Fig.
9.34b
, where the typhoon season and the
following 1-2 months are marked in black with depo-
sition of SDLs and MDLs. The latter can be deposited
in a few weeks after the typhoon season on the basis of
modern sedimentation rates, leaving the other several
months blank or diastems during the non-typhoon sea-
son. Single SDLs can be formed by amalgamation
of several storm deposits over a typhoon season as that
shown in Fig.
9.27
, and only the time intervals B, C,
and D had the corresponding deposits preserved in the
strata, leaving other time intervals blank (Fig.
9.27
).
The temporal distributions of diastems over the
fortnightly and daily intervals were extrapolated from
the tile observations. Meanly five to six sand-mud cou-
plets on the fortnightly tiles and two sand-mud couplets
on the daily tiles denote that 11 out of 14 days and 2
out of 4 semidiurnal tides were blank or without depos-
its over the fortnightly and daily intervals, respectively
(Fig.
9.31c, d
). It is therefore concluded that a sedi-
mentary unit complete on a longer time scale actually
contains many diastems on a shorter time scale.
Diastems in the tidal-flat deposits can be generated by
erosion of storm waves, and also by small waves and
tides. They are discernible or non-discernible, repre-
senting the missing sediment intervals from a few
hours to several years or longer (Fan et al.
2002
).
9.7
Sedimentary Facies
and Successions
9.7.1
Holocene Examples
9.7.1.1
Progradational Open-Coast Tidal-Flat
Successions
The progradational open-coast tidal flats generally
have a convex-up profile with marked fining-landward
intertidal zonations. The regressive vertical stratigraphic
