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 278

Tide-influenced
distributary channel
complex

Coastal plain

Shoreface

Sub-tidal sandsheet

Fig. 21. Conceptual model for the estuarine to transgressive shoreface depositional setting of the Åre Formation.

channels. The tidal deposits alternate with and
grade laterally into marginal-marine interdistrib-
utary bay deposits (FA 7, 8 and 9). The spatial
relationship between the wave-influenced and
tide-influenced deposits is locally challenging to
resolve but the two sub-environments seem to
have been coeval during deposition of some parts
of the succession; suggesting that the wide
mouths of the tide-influenced channels were
closely associated with wave-influenced bay-
margin deltas and more muddy sheltered bay
areas (Figs 7D and 21).

distal expression of the interdistributary bay
environment. The base of the Åre 5 Zone is thus
ascribed to a flooding surface marking a field-
wide transgressive shift to a larger-scale, mud-
prone interdistributary bay setting (FS2; Table 1;
Figs 4 and 18).
The Åre 5.2 Sub-zone is defined by promi-
nent change in facies into a field-wide belt of
tide-influenced distributary channel sandstones
(Figs 18 and 22). Thickness mapping shows that
the base of this channel belt is associated with sig-
nificant down-cutting and a ~ 10 m relief into the
underlying Åre 5.1 Sub-zone has been identified
in the north-western part of the Heidrun Field
(Figs 18 and 23). This erosional surface is
characterised with a basal lag of sub-angular to
rounded intraformational mud clasts overlain by
laterally amalgamated tide-influenced channel
and subtidal flat facies filling in the lowermost
part of the incision (Fig. 22). Amalgamated chan-
nel deposits can be traced for ~ 7 km in E to W
direction and 3km to 5 km in an N to S direction.
In the south-eastern part of the field, the tide-
influenced channel facies grade laterally into
wave-influenced sandy bay-fill deposits (Fig. 18).
Vertically, there is a field-wide facies change from
tide-influenced distributary channel deposits
succeeded by an interval displaying a complex
mixture of tide-influenced and wave-reworked

Åre 5 Zone

The Åre 5 Zone (50 m to 65 m thick) is divided
into three sub-zones based on field-scale facies
changes and correlateable surfaces (Figs 4 and 18).
At the base, the Åre 5 reservoir zone is separated
from the underlying Åre 4 Zone by a field-wide
mudstone (0.5 m to 3 m thick) and an associated
change in facies from sand-dominated bay-fill
deposits below into extensive muddy bay depos-
its above (Åre 5.1 Sub-zone; Fig. 18). This lower-
most sub-zone (Åre 5.1; 20 m to 40 m thick) is
composed of heterolithic to muddy bay-fill facies
displaying crude upward coarsening cleaning
cycles. Compared to the sandy bay system of
the Åre 4 Zone, these facies reflect a more