Updated depositional and stratigraphic model of the Lower Jurassic Åre Formation, Heidrun Field, Norway - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 271

SUBENV .
(FACIES
ASSOCIATION)

LITH
% Sand

GROSS
ENVIRON.

GRAIN SIZE
AND STRUCTURES

LITHOFACIES

DESCRIPTION

Clay silt vf f mc vc gp c

DOMINANT SUBORDINAT E

MI, Mp,
Mr,
MSs(b),
Mro

MSs(r) Dark grey laminated micaceous siltstones, locally with pinstripes, lenses and thin beds of well

sorted coarse silt to very fine sand. Current ripples, wave ripples and occasional
micro-hummocky cross-lamination. Occasional synaeresis cracks. Prominent rooting and
carbonaceous debris, otherwise weak bioturbation, mainly by P. montanus and A. carbonarius .

Bay-margin
muds
(FA 9)

Sp, Sx,
Sscs,
Shcs, Sr

SMs(r),
Ml

Moderately to well sorted, very fine to fine grained sandstones.
Medium-scale (dune) cross-stratification and swaley laminae-sets, plus
planar stratification, wave and current ripple cross-lamination and
hummocky laminae-sets. Sporadic bioturbation by Skolithos,
P. montanus, A. carbonarius and escape traces. May be rooted at top.

Ty pically form upward
coarsening/cleaning-
units. Parts of the
association may occur
as single beds.
Wave-generated
structures dominate,
although current-
structures occur in
the sand-prone beds.

Shcs, Sr,
Sp, Sb1

Sx, SMs
Sg, Sro,
SMb1,
SMb2,
MSs(r)

Moderately to well sorted micaceous very fine to fine grained
sandstones/sand-prone heteroliths dominated by hummocky
laminae-sets and wave ripple cross-lamination. Occasional synaeresis
cracks. Generally weak bioturbation with P. montanus, Skolithos and
A. carbonarius , plus escape and excavation traces.

Mud-prone heterolithic interval with a micaceous quartzose 'sand'
component of coarse silt/very fine sand. Dominated by wave ripple and
micro-hummocky cross-lamination, although larger scale hummocky
cross-stratification occurs. Silt-dominated intervals often show
lenticular bedding. lchnotaxa: P. montanus and A. carbonarius .

SMs
(r,b,l,hcs),
MSs
(r,b,l,hcs)

Shcs, Sr,
Mr, Ml,
Mp, Stb

MI, Mp,
Mr,
Mhcs,
MSs(l,r)

MSs(r),
MSb,
Mv, V,
CMs(l),
Cl

Dark grey-brown micaceous siltstones with thin pinstripes, lenticules and wave-rippled horizons of
pale quartz silt/very fine sand. Occasional micro-hummocky lamination. Synaeresis cracks may
be common and flooding surfaces may exhibit thin coals/carbonaceous siltstones. lchnotaxa:
P. montanus, A. carbonarius prominent. Also Skolithos , resting and excavation traces.

Bay-floor
muds
(FA 7)

Sx, Sp,
Sm,
Sr, Stb,
SMs
(r,b,p)

SMh,
SMb1,
SMb2,
MSs, Mp,
MI, Mv, CI,
CSs(b), Cp

Broad fining-upward/muddying-upward units. Moderately to locally poorly sorted medium to
coarse grained sandstones in the lower part grade up into moderately to well sorted very fine to
fine grained sandstones and sand-dominated heteroliths. Lower to middle parts exhibit
medium-scale cross-stratification and current ripple cross-lamination; upper parts are rippled
heteroliths if preserved. Main ichnotaxa: P. montanus, A. carbonarius , resting and excavation
traces.

Tidally-
influenced
distributary
channel
(FA 6)

Fig. 14. Facies association scheme of the brackish-water interdistributary bay depositional system within the Åre Formation. (See Figs. 6A for legend and
6B for the lithofacies scheme).