Geoscience Reference
In-Depth Information
Table 2.
Heterolithic deposits of the upper Are and Tilje formations. Facies 5 (F5) and sub-facies were classiied on the basis of their sand: mud ratios, thickness, sandstone grain
size, mudstone characteristics, sedimentary structures, and bioturbation style.
Sandstone
grain sizes and
description
Mudstone
description
Sedimentary
structures
Facies 5 (F5): Heterolithics
Thickness (cm)
BI and trace fossils
Interpretation
Facies 5.1 (F5.1)
Sand-dominated heterolithics
(sand : mud ratios 90 : 10 to
60 : 40)
Sandstone
5 cm to 30 cm;
Mudstone
0.2 cm to 2 cm;
Fluid-mud
layers
3 cm to 15 cm,
upward
decrease in
thickness of
fluid-mud
layers.
Very fine to
medium with
occasional
gravel and
pebble lags.
Normal grading
or alternations
between coarse
and fine sand-
stone. Sharp
and erosive
basal contacts.
Continuous paired
laminae/beds
and lenticu-
lar geometries.
Thicknesses
decrease upward
into thin
laminae.
Very thick homog-
enous mud layers
(fluid muds)
occur toward the
base of inter-
vals of medium
and fine-grained
sandstone.
Cross-bedding
and ripple
cross-
lamination
showing
bipolarity.
Stylolites
occur in
the thickest
and coarsest
sands.
BI 0 to 2. Sparse to uncom-
mon. Vertical burrows
in the sandy portions:
Skolithos
and
Dip-
locraterion
. Small-scale
Planolites
within the
laminated mudstones.
Tidally influenced unidirectional cur-
rents with moderate speeds. Paired
mudstones formed by tidal cur-
rents during ebb-flood tidal cycles
(i.e. they represent tidal rhythmites
in which the neap-spring cyclic-
ity is not well developed). High
suspended sediment concentra-
tions (SSC) formed fluid-mud
layers. Upward decrease in thick-
ness of fluid-mud layers indicates a
vertical reduction of the SSC in the
water column (cf. Dalrymple
et al
.,
2003).
Facies 5.2
(F5.2)
Mixed sand/
mud hetero-
lithics
(sand : mud
ratios
60 : 40 to
40 : 60)
5.2.1. (F5.2.1)
Wavy-bedded
current-
dominated
heterolithics
Sandstone
0.5 cm to 5 cm;
Mudstone
few mm
to 2 cm to 3 cm
Fine to medium
with some
coarse-grained
sand and even
granules.
Wavy bedding
styles. Basal
contacts tend
to be sharp or
erosive.
Wavy bedding
styles. Homoge-
neous (com-
monly associated
with the coarsest
sand fraction) or
parallel lami-
nated.
Presence of paired
poorly to more
laminated mud-
stones.
Current-ripple
cross lamina-
tion showing
reverse/bi-
polar direc-
tions.
BI 1 to 3. Sparce to
common.
Paleophycus
,
Planolites
,
Chondrites
,
Skolithos
,
Teichichnus
,
Monocraterion and
Diplocraterion
. BI 3
heterolithics (associated
with fine-grained sand-
stone) alternate with BI
1 heterolithics contain-
ing coarse-grained sand-
stone.
Tidally influenced unidirectional
currents with low to moderate
speeds. Alternation of times of
low and high fluvial discharge.
Homogeneous mudstones asso-
ciated with the coarsest sands
(high discharge) suggest high SSC
and the formation of fluid muds.
(
Continued
)
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