Geoscience Reference
In-Depth Information
Facies 4 (F4):
Hummocky
cross-
stratified
(HCS)
sandstone
(i) Moderately sorted,
very-fine grained,
micaceous hummocky
cross-stratified sand-
stone.
(ii) Well sorted, very-
fine grained, hum-
mocky cross-stratified
sandstone.
Very-fine grained and mod-
erately to well-sorted
grey sandstone. Locally,
sandstones are capped
by sharp-based, 0.5 cm to
3 cm thick, faintly lami-
nated mudstone. Sharp
based and occasionally
erosive. At the base,
locally preserved residual
mud lenses and clasts.
Calcite cement is locally
present.
Amalgam-
ated
bedsets of
up to 4 m.
Individual
bed thick-
ness varies
between
15 cm and
1 m.
Planar and/or
undulatory
lamination,
hummocky-
cross stratifi-
cation (HCS)
capped by
wave rip-
ples, and/or
combined-flow
ripple cross
lamination
with asymmet-
ric round-
crested form-
sets. Weakly
laminated
mudstone on
top of HCS.
BI 0 to 1. Absent to
sparse.
Skolithos,
Diplocraterion
, and rare
Planolites
. Bioturbation
of the capping mud-
stone is top-down post-
depositional. Locally,
vertical to sub-vertical
Glossifungites
towards
the top of HCS beds.
Storm-influenced high-energy
oscillatory currents. Vertical
decrease in wave energy and
turbulence (HCS to wave rip-
ples). Wind-driven residual
currents during storm events.
Superimposed tidal currents.
Wave-generated fluid mud caps
beds.
Facies 5 (F5):
Heterolithics
See Table II
Facies 6 (F6):
Intensely
bioturbat-
ed sand-
stone and
heterolith-
ics
F6.1. Reddish biotur-
bated sandstone
Silty fine/medium-grained
reddish sandstone. Mod-
erately to poorly sorted.
Matrix-supported. Sub-
angular biogenic calcite
grains. Homogeneous
aspect. Mudstone lenses
and interrupted lamina-
tion. Burrow mottling,
small shell debris and
faecal pellets. Iron and
calcite cements.
Bedsets up
to 50 cm.
Occasional
tabular-
stratified beds,
low-angle
lamination
and coarsen-
ing upward
BI 5 to 6. Abundant to
complete. High diver-
sity.
Skolithos
, intergra-
dation with proximal
expressions of
Cruziana
Ichnofacies.
Rosselia
,
Planolites
,
Cylindrich-
nus
,
Skolithos
,
Bergaueria
,
Palaeophycus
, and rare
Thalassinoides
.
Biogenic reworking processes.
Large vertical burrows indica-
tive of relatively high levels of
wave (below fair-weather wave
base but above storm base) or
current energy; developed in
loose or shifting substrates.
F6.2. Disturbed
sandstone
Fine-grained to medium-
grained grey to brown
sandstones. Bedding bet-
ween the sand layers is
distinct but, internally,
trace fossils tend to
cross-cut each other.
20 cm to
40 cm
thick
Cross bedding,
ripple cross-
lamination,
and parallel
lamination
BI 4 to 5. Common to
abundant. Low-diversity.
Archetypal
Skolithos
ichnofacies. Large (10 cm
to 25 cm long)
Diplocra-
terion
, small (0.5 cm to
2 cm diameter)
Planolites
and
Palaeophycus
Moderate to high current energy.
Low diversity but abundant
U-shaped large burrows as a
response to a shifting substrate.
(
Continued
)
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