Geoscience Reference
In-Depth Information
Table 1.
Main characteristics of the key stratigraphic surfaces.
Key surface
Seismic marker
Chrono-strat. age
Surface characteristics
Top Åre 7
Zone
MFS3
No
Early
Pliensbachian
1 m to 1.5 m thick bioturbated and calcite cemented
mudstone/heterolith. Facies transition: from
shoreface deposits of the Åre 7 Zone into
storm-influenced prodelta deposits of the Tilje
Formation
Top Åre 6
Zone
TRS
Yes
n/a
Erosive surface characterised by a reworked lag
deposit and calcite cementation. Facies change:
From tidal to wave-dominated deposits.
A significant shift into more marine trace fossil
assemblage is seen across this surface
Top Åre 6.1
Sub-zone
c.SB3
No
n/a
Sharp and erosive surface with no significant relief.
Facies change: Marks a shift from wave-influenced
bay deposits to tide-dominated deposits
Top Åre 5
Zone
FS3
No
n/a
0.5 m to 2 m thick mudstone or heterolith. Facies
change: A transition from tide-influenced to
heterolithic bay-fill deposits
Top Åre 5.1
Sub-zone
c.SB2
No
n/a
Erosive surface characterised by up to 10 m relief.
Associated with basal lag of mud clasts. Facies
change: From mud-prone, wave-dominated
bay deposits to sandy tide-influenced channel
sandstones
Top Åre 4
Zone
FS2
Local/
segment-scale
n/a
0.5 m to 3 m thick mudstone or heterolith. Facies
change: A transition from sand-dominated to
mud-prone bay facies
Top Åre 3
Zone
MFS2
No
Base/Early
Sinemurian
2 m to 5 m thick laminated, carbonaceous mudstone
and claystone associated with calcite cementation
and bioturbation. Facies change: From mixed
coastal plain and brackish-water interdistributary
bay deposits to extensive sand-dominated
bay-fill facies
Top Åre 2
Zone
FS1
No
n/a
1 m to 3.5 m thick brackish water mudstone, locally
alternating with peat swamp deposits. Facies
change: from fluvial channel facies to marginal-
marine bay deposits
Top Åre 2.1
Sub-zone
c.SB1
No
n/a
Field-wide down-cutting of a fluvial channel belt.
The surface is associated with a pebble lag and
variable relief
Top Åre 1 Zone/Coal
Marker
MFS1
Yes
Middle Hettangian
10 m to 46 m thick package of peat swamp coals and
lacustrine mudstones. Facies changes: Marks a
change in fluvial channel stacking pattern and
a shift from wet and immature to better drained
floodplain palaeosols
either flooding surfaces (FS), maximum flooding
surfaces (MFS) or transgressive ravinement sur-
faces (TRS) (cf. Galloway, 1989; Posamentier &
Vail, 1988; Van Wagoner
et al
., 1988) as specified
in Fig. 4 and Table 1. In core, the deepening
events are recognised as 0.5 to 5 m thick mud-
stone-dominated intervals (Fig. 8) characterised
by bioturbation (onset of brackish or marine
water ichnofabrics) and, in some cases, calcite
cementation (e.g. MFS2, TRS and MFS3; Table 1
and Fig. 8). According to Hammer
et al
. (2010)
the calcite cemented beds associated with key
Key stratigraphic markers
The most reliable correlative markers within the
Åre Formation are various flooding surfaces
which form the basis for the stratigraphic analy-
sis provided here. Within the Åre Formation on
the Heidrun Field these are not
sensu stricto
parasequence-bounding flooding surfaces (Van
Wagoner
et al
., 1988), but they are ascribed to
relative deepening events marked by condensed
deposits and field-scale shifts in depositional
style. These transgressive events correspond to
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