Page 50 - Carbonate Platforms Facies, Sequences, and Evolution

ence
Shoal
in the
Works
measured
constitute
individual
individual
(Fig. lOa)
dimension
N
Description
surface.
the
of
Quarry
shoal
shoal
sequences
The
the
southeastern
at
·'
Microfacies 1: Bioclast
perpendicular
Pin
provides
shoal
sequences
architecture
absence
a
to
face of
sequences,
lOrn thick, they are between
of
Dale
the
the
the
Hope
of this
MICROFACIES
means
and
sequence.
-
shelf
underlying
200 and
of
.......
shelf
shoal
shoal
Hope
Cement
bedforms
-
These
700m
margin
margin
tinguished, their distribution is shown in Fig. 9.
that the shoal sequences have a sheet-like form
extend at least 300m parallel to the shelf margin.
Sequence
peloid intraclast grainstone
produced them and the three-dimensional relation­
This microfacies is a grainstone with localized pack­
=
stone texture. It contains a diverse allochem assem­
this emerg­
their microfacies. Four microfacies have been dis­
Quarry places a minimum value for the along-strike
which
wide
Works
sequence
together with information from quarry faces, suggest
ships between the shoal sequences which together
correlation
be placed upon the three-dimensional form of the
complex.
between the two exposures and allows constraints to
of the shoal sequence in Pin Dale and Hope Cement
The main palaeokarstic surface developed at the top
Works Quarry (shoal sequence 3) were sampled for
blage (Table 1) dominated by brachiopods, crinoids
Cement
data,
and
Sub-sequence
Boundary
This
ment
clasts
filling
-
tation.
Boundary
bioclast
granule
bioclast
uniform
shelf interior
followed
rounding
bioclasts,
complete,
fragmented
well-sorted,
graded and
show
This
by
Platform-margin bioclastic shoals,
Allochems
bioturbation.
size.
foraminifera,
sparry
micritization.
are
Interpretation
of shell
a
peloid
in
_:.::-
and
the
microfacies
UK
which,
All
thickness.
algae
high
assemblage
precedes
Peloids,
grain-size
of lower sub-sequence and marked erosional truncation at the upper sequence boundary.
cement.
and
abundant
fragments.
Some
concentrically
contains
together
bioclasts
grainstone
degree
microfacies
a
This
and
varies
1
precipitation
formed
ment and frequent reworking.
of
are
aragonite
There
are moderately-
Covered Section
dominated
with
type C: bioclast wackestone (Fig.
of
(Fig.
by
are
is
oncolites.
to
a
range
by
from
specimens
diverse
the
laminated
crinoids, bryozoans and foraminifera.
lOd).
in
The
s
lOb);
are
poorly
open
radial-fibrous
dissolution
have preferential sub-horizontal
ferroan
Fig. 8. Line drawing of the lower part of the quarry face at Bradwell Dale (SK173807), illustrating bedding plane
size
to
fragmentation
cement is also found within type A intraclasts.
disarticulated
coating
type
fine-sand
micritization
no evidence
and
All the bio­
grainstone texture, suggest a high energy environ­
configurations, sequence boundaries and sub-sequence boundaries. Note symmetrical upbuilding and mound-shaped form
align­
pore­
However, sedimen-
llb) is locally present as the initial phase of cemen­
from
medium sand to granule. Oncolites (Fig. lla) have a
bioclast or peloid nucleus around which there is a
and
of
well-rounded.
Grain roundness increases with increasing degree of
normally
B:
calcretized bioclast grainstone-packstone (Fig. lOc);
very
to
calcite
of
following
An isopachous radial-fibrous calcite cement (Fig.
and peloids. Minor constituents include bryozoans,
of
three intraclast types are also present: type A: sorted
and
45
brachiopods,
marine
predominant
is