Page 76 - Carbonate Platforms Facies, Sequences, and Evolution

68
In
from
simply
the
subsidence.
Strudwick
sequences.
and
general
for
the
(1987,
predicted
the
first
fig 7 .2)
program
eustatic
time,
how
pattern
'Walther'
of
G.M.
Leeder
triggered reversals can be an impressive simulation
demonstrates
of the facies diversity seen within actual cyclothemic
delta-marine
and show that in all but
distal situations a limestone-shale boundary should
&
eustatic regime. The synthetic cyclothems are distinct
interactions of the Yoredale type can result from an
Walkden and G.D.
duction
quences
normally
of
be
a
Walkden
produced
delta
by
lobe.
diachronous
the
to contain elements of each.
rather
three
Evidently
than
the
processes
of different cycle magnitudes on facies development. Facies are numbered as in Figs 11 & 12. Variables as follows:
erosive
in both runs is the same. Note that the best development of delta-top facies occurs where there is added compactive
facies
subsidence rate 3 em kyr- 1 , sedimentation rate lO cm kyr- 1 , cycle period 400 kyr. (a) A cycle magnitude of 20 m and delta­
top facies are poorly developed. (b) A magnitude of lO rn and delta-top facies are well developed. Delta development rate
by rapid tectonic subsidence alone followed by intro­
se­
believed by Leeder & Strudwick (1987) to be charac­
Fig. 13. Two runs of 'Walther 2' (asymmetric wave) together with enlargements of the sediment column to show the effects
and
teristic only of the patterns produced by avulsion or
coals are a usual component. These features were
difficult to distinguish and the real situation is likely
remain