Page 66 - Carbonate Platforms Facies, Sequences, and Evolution

of
58
the
run
This
menu.
the
in
a
Objectives
THE
presentation
Reasonable
sedimentation
be allowed to
program
eustatic
completion
Other variables,
and
sediment column,
lag
to
vary
curve
default
the
scope
times,
demonstration
simulates
PROGRAM
are
top
are
are
versions of specific programs.
values
randomly
of
mode
at
are
are similar to those of Read et al.
featured
the
distinct.
successions where a main controlling
in
preset
shallow-water
directly
G.M.
given
The
screen
to
'CYCLOTHEM'
values
of
user­
purpose of the program was to determine the influ­
within preset limits.
set at actual time or thickness values and some can
must be changed by accessing the program. One or
and
descendent
two more important modifications such as the form
defined variables which enable the programs to be
loading. At the conclusion of a run, determined by
the
following
such as sediment compaction and
parameter is
the screen can be saved on disk
carbonate
likely to be water depth. The underlying objectives
subsidence and eustatic cyclicity on the generation
for reloading later or the user can return direct to
ence of differing rates and patterns of background
of 10m-scale, 200-600 kyr marine cyclothems of the
(1986) although
original
fail
sort
Walkden and G.D.
1979;
et al.,
(1986)
Late
the
cessions
modelled
seen
Dinantian
sequences
(Walkden,
equivalent
Anderson,
for
1978;
by
in
Goldhammer
or
(Ramsbottom,
Walkden
and
1987;
Walkden,
the
the
Dinantian
late
containing
cyclothems
1973;
Burgess
(1988)
carbonate
previous
late
are
1987).
Leeder,
1985; Heckel,
Lower
Visean)
for
On
still
Lower
authors
well-developed
Walkden,
the
the
& Mitchell,
successions
such
ingly being ascribed to glacioeustacy
sedimentation rates.
of Britain
clastic-carbonate
1974;
observed
as
Proterozoic,
1976;
(e.g.
exposure
relates to their respective
in
settings of all user-defined
typical of late Palaeozoic cycles (e.g. Heckel,
Ordovician
Carboniferous
cyclicity is most obvious in
x:y ratio of the subsidence line
The screen displays the current
Read
Euramerican
(Goodwin
defined facies, and 'Depos. rates'
Goldhammer et al. (1987) for the Middle Triassic.
and 'Subsidence riser' relate to the
'Depth ranges' relates to the depth­
variables. 'Magnitude' and 'Period'
(1989) have made a distinction between eustatically­
generated Kansas-type cyclothems and tectonically­
which is drawn in steps if required;
worldwide scale, Carboniferous cyclicity is increas­
suc­
(late
1986)
but is up to an order of magnitude longer than that
surfaces.
refer to the cycle; 'Subsidence tread'
and
& Strudwick, 1987) although recently Leeder (1988)
&
Fig. 3. Menu screen of 'Cyclothem'.
1988). This periodicity is
to
mechanisms for Carboniferous minor cyclicity (Bott
there is strong support for tectonic and autocyclic
Grotzinger
1987; Walkden, 1987) and recently Klein & Willard
Somerville,
generated Appalachian-type cyclothems. In the UK
interactions
1987). They are characterized by shallowing-up facies
Walkden,
&
laterally
Mitchell
and Europe
of the Yoredale type (e.g. Johnson, 1972; Walkden
& Davies, 1983), but where the clastic components
1986; Veevers & Powell,
& Johnson, 1967; Johnson, 1984; Bott, 1987; Leeder