Geoscience Reference
In-Depth Information
Stage 1
Stage 2
Sediment source
Ribble Mb. Sediment source
SW
NE
SW
NE
Erosion
Jurassic
Jurassic
Triassic
Triassic
Salt
Salt
Ribble Member Turbidite sandstone
Rotliegend
Rotliegend
- Jurassic reactivation of Triassic pod
- Continuing salt withdrawal
- Deposition of fluvial Middle Jurassic or
Upper Jurassic shallow marine sandstone
- Grounding of pod on Rotliegend
and inversion of rim synclines
Stage 3
Stage 4
NE
SW
SW
NE
Cretaceous
Kim Cl.
Jurassic
Jurassic
Kim Cl.
Triassic
Triassic
AUK
HORST
Salt
Salt
Rotliegend
Rotliegend
- Erosion and development of Late Cimmerian
Unconformity
- Reactivation of graben margin fault
- Internal sliding/creeping and soft sediment
deformation
- Onlap of Cretaceous sediments and burial
Fig. 10.
Time step progression showing the development of a tectono-sedimentary setting of 'Type B - Reactivated Pod
Setting'. The example comes from the Fulmar Field (adapted after Johnson
et al
., 1986). Marine shales and transition zones
siltstones are shown in blue. Shoreface sandstones are shown in yellow. Reworking of previously deposited shoreface
sandstones can occur on top of the structure following pod grounding. This model is based on examination of correlations
made by Kuhn
et al
. (2003). The reworked shoreface sandstones were re-deposited to the west as turbidites of the Ribble
Sandstone Member. The location of this section is indicated on Figs 1 and 8.
the grounding of Triassic pods occurred relatively
early. On the West Central Shelf for example
(Fig. 1), grounding occurred before the Mid-
Triassic (Fraser
et al
. 2002). The grounded
pods were surrounded by salt highs which were
differentially eroded leading to the development
of salt cored valleys. These valleys were flooded
during the Upper Jurassic after a long period of
exposure, in the order of 80 Ma according to
Rattey & Hayward (1993) and they became
commonly infilled with Upper Jurassic littoral
sandstones (Fig. 9). Examples of Type C tectono-
sedimentary setting have been described from
the Durward and Dauntless fields (Stewart
et al
.,
1999).
extension took place on basement faults that may
show local displacements of up to 3 km (Stewart,
2007). This implies rapid rates of extension and
subsidence during the Late Jurassic and conse-
quent important evolution of the location of sedi-
ment sinks. Rifting occurred initially in the most
central parts of the basin such as the East Central
Graben and the Feda Graben and extended gradu-
ally towards the margins of the basin. This led to
major shifts in shoreface sandstone depocentres
both in the UK sector (Fig. 9) and the Norwegian
sector (e.g. stratigraphic evolution from well 2/4-
20 to well 2/1-4 shown in Fig. 5).
CASE STUDIES
Regional structural controls on deposition
Case Study 1: NO-2/4-14 well area:
Type A - Hangingwall trapdoor setting
In addition to local structural controls such as
those described above, there are also regional
changes to consider due to the overall develop-
ment of the Central Graben rift. Upper Jurassic
Examples of the Type A hangingwall trapdoor
tectono-sedimentary setting are abundant in
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