Geoscience Reference
In-Depth Information
Table 2. ( Continued )
Facies type
Characteristics
Log motif
Depositional process
Depositional geometry
Ripple cross-
laminated
sandstones
Thin, erosively based, normally
to ungraded, medium to fine
grained, and occasionally
coarse to granule sandstones
that form thin caps to under-
lying sandstones.
Tractional movement
of ripple trains as
bypass lags
Bed cappings in inner
and central part
of lobes; bypass
indicator.
9
Disorganised
granule
sandstones
Sharp, erosively-based and
sharp-topped, thin-bedded
to medium-bedded, massive,
disorganised granule sand-
stones. Sometimes ripple
cross-laminated.
Rapid dumping and
winnowing from
high-density sedi-
ment gravity flows
as bypass lags.
Channel- and scour-
base lags in inner
fan distributary
channel and chan-
nel-to-lobe transisi-
tion zone; bypass
indicator.
10
Disorganised
mud-chip
sandstones
Sharp, erosively-based, thin-
bedded to medium-bedded,
massive, disorganised matrix-
rich sandstones with abundant
floating mud granules and mud
chips. Bed/set tops are sharp or
amalgamated.
Rapid dumping from
highly erosive
high-density sedi-
ment gravity flows.
Channel-mouth,
channel-to-lobe
transition and inner
lobe irregular units.
11
Clay clast
conglomer-
ates - bed
base clus-
ters
Clast-supported to matrix-
supported conglomerates with
cm-sized angular claystone
rip-up clasts floating in a
sandstone matrix composed
of poorly sorted, ungraded,
coarse to medium grained
sandstone, often with abun-
dant clay chips.
Rapid dumping from
highly erosive
high-density sedi-
ment gravity flows.
Channel-base lags
and channel-margin
collapse breccias.
12
Clay clast
conglom-
erates -
clustered
floating
clasts
Matrix-supported and clast-
supported conglomerates
with cm-sized subangular
to rounded claystone rip-up
clasts floating in upper part
of beds or as bed cappings.
Matrix composed of medium
sorted, ungraded, coarse to
medium grained, clay matrix-
rich sandstone.
Rapid dumping from
high-density sedi-
ment gravity flows;
clasts kept aloft by
dispersive pressure
and high grain
density.
Localised bed cap-
pings and intra-bed
pockets.
13
Mud-rich
silty
sandstones
'Dirty', commonly structureless,
pebbly sandstones with
abundant mudstone matrix.
Pebbles are dominantly
fragmented, angular to sub-
rounded claystones and
mudstones. Wispy lamination
indicative of post-depositional
dewatering and slumping
locally present.
Frictional freezing
of debris-flows
deposits, or col-
lapse of muddy
flows to form
so-called 'slurry-
flows', in some
cases followed
by early post-
depositional
gravitational
deformation as
a 'flow-slide'.
Elongate tongues and
fringes of lobate
beds.
14
 
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