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commonly delineate reservoir zones, but in some
cases define reservoir subzones (Fig. 4).
topped, completely sand-dominated and lack ver-
tical trends in grain size (Fig. 12). This channel-fill
style may imply that deposition occurred in
downstream accreting bedforms. Interpretation of
fluvial channel style based upon vertical profiles
from subsurface well dataset is inherently prob-
lematic. However, for the purposes of reservoir
characterisation, this simple twofold subdivision
of channel sandbodies is used to group and model
the key elements of the reservoir.
The floodplain deposits within the Åre 1 and 2
Zones are dominated by dark grey-brown clay-
stones and siltstones with coals (Fig. 9). The coals
are dm-thick to m-thick beds of vitreous coals or
siltstones with high volumes (30% or more) of
carbonaceous debris (FA 1; Fig. 10). Pedogenic
mottling and rooting is well developed within
these peat swamp deposits and they are com-
monly associated with claystones and siltstones
with palaeosol character (FA 3). Locally, the
extensively rooted horizons of siltstone and clay-
stone of FA 3 underlie thin coals/carbonaceous
siltstones (FA 1) and are therefore regarded as
'seat-earths'.
Lacustrine mudstones (FA 2), a common ele-
ment of the floodplain deposits (Figs 9 and 10),
are dominated by laminated to pinstriped silt-
stones and claystones. Fine carbonaceous debris
Åre 1 and 2 Zones: Fluvial/alluvial
coastal plain
Fluvial coastal plain deposits of the lower Åre
Formation (Åre 1 and 2 reservoir zones; Fig 4)
are up to 470 m thick. Facies associations are
classified as: fluvial channel (FA 5), crevasse
splay (FA 4), palaeosol (FA 3), lacustrine mud
(FA 2) and peat swamp (FA 1; Figs 9, 10 and 11).
Fluvial channel deposits (FA 5) from the lower-
most part of the Åre Formation have been cored
extensively and two main types of channel-fill are
recognised: 1) thin (3 m to 5 m), sand-rich single-
story channel belts and 2) thick (5 m to 35 m),
multi-storey sand-dominated channel belts that
display frequent internal scour surfaces. Single-
story channel belt deposits are characterised by
erosive basal boundaries, fining-upward grain
size trends and, in their upper parts, inclined het-
erolithic strata. An upwards decrease in bedform
scale (from dune-scale to ripple-scale cross bed-
ding) and grain-size reflects waning current
strength due to lateral migration of a channel mar-
gin and adjacent point bar. Multi-storey channel
belt deposits are both sharp-based and sharp-
SUBENV
.
(FACIES
ASSOCIATION)
GROSS
ENVIRON.
LITH
% Sand
GRAIN SIZE
AND STRUCTURES
LITHOFACIES
DESCRIPTION
DOMINANT
SUBORDINATE
Clay
silt
vf
f
mc
vc
gp
c
Sx, Sp,
Sr
Sd, SMd,
Mp, SMs
(p,r,x), Sro,
SMro, Mro,
Mv, V, Sg
Moderately to well sorted, locally poorly sorted, fine to medium
and, locally, coarse-grained sandstones, passing upwards into
very fine to fine grained sandstone. Lag deposits of mudstone
clasts, quartz and coaly debris occur. Vertical decrease in the
scale of cross-stratification. Upper parts may be heterolithic.
Fluvial
channel
(FA 5)
Stb, Sr,
SP,
SMs(p)
Sx, Sd,
Ml, SMro,
Mro, Cro,
Mv, V, Cl,
SMb1 & 2
Thinly bedded, moderately to well sorted, very fine to fine, locally
medium grained sandstones. Silty/argillaceous in the upper parts
of the beds. Mainly ripple cross-laminated, often over-printed by
pedogenesis. Interbedded with claystones, siltstones and thin
coals.
P. montanus, Ta enidium
and general burrow mottling.
Crevasse splay
complex
(FA 4)
Cped,
Mped,
Cro, Mro
SMro, MI,
Cl, Mv,
Cv, V
Mid to dark grey-brown claystones and siltstones exhibiting a
mottled pedogenic fabric. Often preserves carbonaceous roots
and may include thin coals/carbonaceous siltstones.
Occasional
P. montanus
and
Ta enidium.
Palaeosols
(FA 3)
Ml, Cl
MSs(r)
Mh, Ch,
Mp, Md,
Mped,
Mro, Cro,
Cp, Mv, V
Mid to dark grey-brown claystones and siltstones. Horizontally
laminated with occasional pinstripes. Occasional rootlets and thin
pedogenically-modified horizons.
Lacustrine
muds
(FA 2)
Mv, V
Mro,
Mped,
MI
Common coal deposits with significant 'seat-earth' development
in pedogenically-modified siltstones and claystones. Frequent
preservation of carbonaceous roots. Occasional laminated
claystones/siltstones. Local sphaerosiderite.
Peat swamp
(FA 1)
Fig. 9.
Facies association scheme of the fluvial/alluvial coastal plain depositional system within the Åre Formation.
(See Fig. 6A for legend; and 6B for lithofacies scheme).
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