Page 48 - Carbonate Platforms Facies, Sequences, and Evolution

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Dale. For the location of the log see Fig. 4.
limestone
mudstone
shell fragments
-paleokarst
-paleokarst
-paleokarst
-paleokarst
-paleokarst
crinoid fragments
Fig. 5. Graphic log showing the sedimentological
sub-sequence
sub-sequence
aligned crinoid stems
limestone
1
2
expression of the shoal sequence and sub-sequences in Pin
to
of
by
are
dip
this
at
the
bedform
represent
indicating
indicating
basinward-
geometry.
transport.
concave-up
clinoforms.
present
a
Platform-margin bioclastic shoals,
stratification
sequence
successive
shelf
20-22°
crest.
is
thinly-bedded
UK
cross-stratification
cross-stratification
within
and
section
reworking
basinward
geometry
Bradwell Dale (Fig. 8)
margin.
with
boundary
this
clinoforms
a ' nd
contain
Form of the shoal sequences
superimposed
dips
cosets
transport.
contain
on
superimposed
up
perpendicular
Small-scale
of sediment by
on
tabular cross-stratification with cosets
to
sub-sequence.
during deposition of this sub-sequence.
these
to
bottomsets
shelfward
(0.05-0.1 m) crinoidal
rents perpendicular to the bedform crest.
up
a
Shelfward
superimposed
the
ripple
at
are
0.2 m
to
bimodal
rhizocretions
=
cur­
well­
clino­
forms is locally developed with palaeocurrents in­
cross­
developed (Figs 6 & 7b). Several truncation surfaces
indicating both accretion and basinward progradation
Clinoforms within the higher sub-sequence have a
Small-scale
and shelfward-dipping clinoforms which
margin. One shoal sequence is exposed, containing
shoal complex oriented perpendicular to the shelf
and
calcrete mottles indicating that the lower bounding
former
bedform with the development of tabular to convex­
dicating basinward transport of sediment down the
15°
surface was emergent prior to bedform development.
The locus of the topset-foreset transition marked
43
clinoforms dip at 8-12° and contain superimposed
in a shelfward and basinward direction. The crest of
grainstone-packstone. The clinoforms dip 12-14°
Bradwell Dale provides a section through part of the
the bedform trends 115-295°, which is sub-parallel
Two sub-sequences are recognized
within this shoal sequence on the basis of clinoform
The lower sub-sequence represents the early stages
bioclastic
of bedform growth and is a symmetrical upbuilding
to 0.5 m in thickness. Basinward dipping clinoforms
up shelfward and basinward dipping clinoforms up
dipping
thick
clinoforms
The higher sub-sequence is marked by a change
from vertical aggradation to lateral accretion of the
The term 'form' is used to describe the shape of the
thick indicating alternate shelfward and basinward
tabular
0.2 m