Page 46 - Carbonate Platforms Facies, Sequences, and Evolution

the
the
has
only
of the
caused
graphical
formities.
Stevenson
Horsfield,
local
shoal
not been
&
initiation
Gaunt, 1971).
The
Derbyshire
1940;
of
Midlands (Fraser
poorly constrained.
reactivation
which are bounded by
an
Gaunt,
significance
of
Eden
significance
surfaces. Internally, shoal
discussed.
of
sequences are relatively well
in
probably been overstated.
et
carbonate
two main sub-sequences, often
principal building blocks of the
of the shoal sequences and sub­
parallel to the shelf margin, are
1971).
unconformities, often paleokarst
sequences can be subdivided into
of the shoal complex, particularly
the
et at., 1990).
al.,
shoal complex are shoal sequences
elements of the shoal complex and
their approximate dimensions. The
intrashelf
Fig. 3. Diagram illustrating the main
It
geometry. Note that the dimensions
constained, whereas the dimensions
marked by a change in the clinoform
basement
terms
Asbian-Brigantian
of
1964;
basin
platform
The sequence
faults
follows
the
'
'
'
I
"
boundary
from
unconformities
,' ' , ,
' ' '
'
resulting
Stevenson
'
,
?
'
Asbian-early Brigantian episode of tectonism cor­
identified in this study have been interpreted pre­
viously as major non-sequences and angular uncon­
Such previous studies have concen­
complex and that the regional strati­
1987, 1989). Regional work on Dinantian basins in
boundaries
the subsurface and at outcrop shows that this late
study that many of these sequence boundaries have
has
(Gutteridge,
this
responds with the EC5 seismic sequence in the east
been correlated with one of the sequence boundaries
of the bioclastic shoals whereas their sedimentology
in
trated on stratigraphical and palaeontological aspects
The bioclastic shoal complexes have been referred
has
evolution
underlying
described here from Pin Dale (e.g. Eden et al., 1964;
to as 'fiat-reefs' by previous workers (e.g. Shirley &
&
'
SUB-SEQUENCE
' ,,
1 '
SHOAL
of
,.. .......
< •
and
· · �
��"1'
'
ometries
geometry
sequences
truncation
' , ,
recognized
of
Platform-margin bioclastic shoals,
:':·:·:�
vertical
sedimentary
which
UK
where
INTERNAL
these
bedding
style
SUB-SEQUENCE 2
SHOAL
implies
there
relationships
a
is
during
sequences
SHOAL
accretion of the shoal sequence.
and
COMPLEX
change
GEOMETRY
/
configurations.
/
Our approach is illustrated by Fig. 3.
the
evidence
'
COMPLEX
in
I
I
'
..,..
deposition
provide
OF
of
The
' ,
the
..
of
a
' ,
a
complex has been divided into a number of
?
'
internal
THE
'
shoal
/
'
style
'
'
300�
'
'
'
se­
ge­
Application of a sequence stratigraphic approach in
this study has enabled the recognition of a number
of sequences within the shoal complex. The lateral
important
information on the evolution of the shoal complex.
quences are several tens of metres thick and several
bioclastic grainstone and associated facies as a whole.
shoal
sequence. This is usually seen as a change in clinoform
hundred metres in lateral extent. Sub-sequences are
change
recognized by downlap, onlap, toplap and erosional
of
margin and forms a belt 1-2m wide. The thickness
of the complex is between 50 and 100m. The shoal
The term shoal complex refers to the shelf margin
It is exposed for at least 3 km parallel to the shelf
I
I
41
which are separated by sequence boundaries
shoal
)
3om f.-1 oom
.