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8130
8083
8037
8027
8010
7970
7928
7884
7840
SW
NE
18648
18795
18934
19071
19205
19340
18250
18380
18511
2/4-14
-1500
Tu rbidite sst
+0
Shoreface sst
+1500
200ms
TWT
Salt
10 00 m
ms TWT
+3000
Fig. 11.
Genetic sequences showing onlap associated with MFS in the vicinity of the 2/4-14 well. Onlapping
strata mark renewed clastic influx in an overall shaley succession. The location of this section is indicated on
Figs 1 and 8.
the Viking Graben area but less common in the
Central Graben where the presence of Zechstein
salt and Triassic pod development generally cre-
ates a more complex structural setting. However,
where salt thickness is limited and Triassic pod
grounding occurred relatively early (i.e. prior to
Jurassic), the Jurassic deposits form a deposi-
tional wedge with a geometry that is primarily
influenced by the movement of Rotliegend fault
blocks (Fig. 11).
In Type A settings, Middle and Upper Jurassic
deposits thin towards the crest of the fault block
and genetic sequences defined by MFSs show
stratal onlap on seismic sections. Such tectonically
controlled onlaps have now been widely docu-
mented form the North Sea rift basin (e.g.
Underhill, 1991). Within the Kimmeridgian suc-
cession, onlapping strata mark renewed clastic
influx in an overall shaley succession. Onlaps are
often associated with turbidite 'ponding' in struc-
tural lows. The J62 MFS in the example shown in
Fig. 11, the King Lear discovery (Jones
et al
., 2013)
is overlain by hydrocarbon-bearing turbidite
sandstones that are calibrated by wells NO-2/4-14
and NO-2/4-18R (Mjelde, 1991; Landrø, 2011).
Dipmeter data from the 2/4-18R well suggest that
these turbidite sandstones were sourced from the
North and deposited within a basin depocentre
oriented NW-SE, following the structural trend
imposed by the underlying major Rotliegend
faults. The turbidite sandstones bodies (T4/T2
facies; 5 m to 20 m thick) are of varying quality
and occur as a multi-story succession up to 120 m
thick. Lateral continuity is variable, but some
thicker sandstones extend for at least 1 km.
This type of tectono-sedimentary setting pro-
duces stratigraphic series that are relatively layer
cake in geometry but wedging away from major
sub-basin boundary faults. Hangingwall onlap
related to phases of rapid fault movement is a
characteristic feature and an important control on
the geometry and geographical localisation of
sandstone bodies. Erosion on the crest of fault
blocks can be anticipated, which may cannibalise
older stratigraphy. However, late erosion at Base
Cretaceous Unconformity (BCU) level may mean
that any stratal evidence for earlier phases of ero-
sion is removed.
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