Page 113 - Carbonate Platforms Facies, Sequences, and Evolution

the
terms
The
errors
It is
figures,
sidence
paction
(notably
of
1000yr- 1
in
level rise.
typical
extensional
subsidence.
particularly
and
Muschelkalk
and
the
and
If
simply
instructive
regional
minimum
the
basins.
4cm
eustacy.
subsidence
level rise is implicated.
here
problems
the extensional phases and
interesting
Fig. 24. Schematic graph of
uncertainty
values,
to
cumulative sediment thickness
of
to
of
rates
(decompacted) against time, with
calculating
subsidence
are
1000yr- I ,
depositional sequences also shown.
Although
the
If the figures
sedimentation
the
note
consider
are
and/or
f-
f-
f-
w
z
0
<t:
Q_
w
(/)
w
w
w
w
z
0
f=
:::;
::J
8
0
...I
0
:::;
(/)
::J
<t:
:.::
>
0
0
r
:::;
0
(/)
there
mentioned
rates
the
same
amount
respectively.
are
are
800
0
sedimentation
200
600
400
non-deposition,
1000
of
similar,
eustatic
245
above
order
com­
for sediment. The accommodation depends on sub­
sea­
higher than the subsidence rates, then a eustatic sea­
rates
tract of the Lower Muschelkalk can be explained in
much
really quite low (4 cm 1000 yr- 1 ), but this probably
involved), it is useful to compare these figures with
(Benifallet Unit) was deposited close
apparent
many
reflects the accommodation, i.e. the space available
These
HST-1 of the Lower Muschelkalk are around 20 cm
of
magnitude as those for regional subsidence, and it is
time
then
reflects the time required to fill the basin. Rifts are
commonly starved of sediment in the early stages as
1985). The sedimentation rates for the TST-1 and
a result of the rapid subsidence (Pitman & Andrews,
to sea-level, the sediment thickness very accurately
sedimentation
sedimentation rate for the Buntsandstein is
for
the sequence could be explained simply in terms of
Buntsandstein through to the lower part of the Upper
rates (see Table 1, Fig. 24). Since much of the upper
a
LST
by
the
rifting
(Figs
being
Upper
Upper
decline
due to
time
pattern
regime:
Thus,
changes.
24
formation
sequences
in
of
deposition
of
240
synrift
-
&
regional
Muschelkalk
two
Muschelkalk,
as
Middle Triassic carbonate ramp systems,
subjected
close
25).
(see
and
to
to
available,
subsid.
phases
Muschelkalk,
Spain
Muschelkalk,
extension.
simply
Considering
The
TIME (Ma
)
Fig.
a
it
the
a
of
then
subsidence,
sedimentation
sedimentation
is
the
fact
The
6 em
Buntsandstein
24).
in
the
same
sea-level
rate
235
that
some other mechanism is
the
facies
and
response
somewhat
This
reason
possible
and
extension,
depositional
permitting
synrift
sequence -2
HST
thermal
to
1000 yr- 1
two
to
these
thermal rift --subsidence
for
through
area of rapid subsidence at base level.
the
more
could
each
the
perhaps
extensional
postrift
and
the
sequence
this
Middle
Lower
rapid
in
Again,
explain
is
sidence rates, and they also decrease with time.
ability
deposition
reflect
rift --
decreasing rate of thermal subsidence after the ex­
1000 yr- I , respectively, are similar to regional sub­
bearing in mind the limitations of the in­
Mus­
over the whole of western Europe in the Germanic­
2·5 em
tension. In Depositional sequence 2, Middle through
the
evaporites to be precipitated quickly and so keep an
followed
and
Lower
chelkalk followed by the postrift Upper Muschelkalk
a
sedimentation rates of the TST-2 and HST-2 in the
Upper Muschelkalk, it is noteworthy that there is a
depositional
Lower
the
high sedimentation rate for the Middle Muschelkalk,
230
103
required
Middle Triassic depositional cycles can be correlated
type Triassic is simply a result of the whole region
tectonic
the
of
rise
of
the
tectonic
regime. It does not require global eustatic sea-level