(a) Location of the study area. (b) Structural elements within the study area,
including wells applied in this study (CG – Central Graben; DCS – Danish Continental
Shelf; CSFC – Coffee–Soil Fault Complex; EB – Egersund Basin; FFZ – Fjerrislev Fault
Zone; HG – Horn Graben; KFZ – Kreps Fault Zone; LFB – Lista Fault Blocks; NCS –
Norwegian Continental Shelf; NDB – Norwegian Danish Basin; RFH – Ringkøbing Fyn High;
SG – Skagerrak Graben; STZ – Sorgenfrei Torquist Zone; ÅG – Åsta Graben). See
correlation between Norwegian wells 11/10–1, 9/12–1 and 2/2–2 in Figure 4. (c) Seismic data coverage available for this study
(courtesy of Fugro Multi Client Services and TGS Nopec).
Sketch summarizing the four T-R sequences described in this study and the
corresponding sequence boundaries (SB), transgressive surfaces (TS) and maximum
flooding surfaces (MFS). Note the non-accretionary nature of the TST of OSS-1 and
OSS-4, while the TST in OSS-2 and OSS-3 are aggradational. The sketch is not to
Seismic stratigraphic sequences correlation with the NSA zonation of King (1989) and Gradstein & Bäckström (1996), correlated to that by Michelsen
& Danielsen (1996) and Jordt,
Thyberg & Nøttvedt (2000). Arrows
indicate direction of sediment progradation.
(a) Time-thickness map of OSS-1. The clinoform facies for the various units
represents the highstand systems tract and also the main depocentre at the time of
deposition. (b) The upper surface of OSS-1 is marked in red in the seismic section
(B–B’). (c) Seismic termination above offlap break, indicating clinoform toplap
(a) Base map showing salt structures in the study area penetrating and/or affecting
the Oligocene sequences. Seismic sections showing halokinesis during deposition of
(b) OSS-1 and (c) OSS-3. Arrows mark seismic onlap against the salt structures.
Arbitrary seismic sections (striking NNE–SSW) illustrating the various systems
tracts of the Oligocene sequences. Note the onlap pattern of OSS-1 against Eocene
strata in the NE part. See Figure 1 for
location of the seismic lines.
Seismic examples including well tie to well 11/10–1 and the prograding RSTs in the
western part of the main depocentre relative to sequences (a) OSS-1 and (b) OSS-2.
See Figure 7 for line locations. Note that
OSS-1 onlap Eocene strata towards the north, whereas OSS-2 has a more uniform
(a) Time-thickness map of OSS-2. (b) Clinoform facies for the sequence represents
the highstand systems tract and is coherent with the main depocentre at the time of
deposition. (c) Internal erosional surfaces in the seismic section and incision at
the upper SU.
(a) Time-thickness map of OSS-3. (b) Clinoform facies for the sequence represents
the highstand systems tract and also the main depocentre at the time of deposition.
(c) The TST and RST are separated by a MFS.
Summary of sea-level changes and regional subsidence during deposition of the
individual sequences from this study compared to the eustatic sea-level changes
proposed by Kominz & Pekar (2001).
Note the vast sediment volume rate in OSS-4.
Position of the main depocentres of the OSS-sequences and illustration of
drainage pattern during Oligocene time. Uplift of southern Norway may have forced
the drainage system eastwards, with the result of sediment transportation mainly
from the NNW and north during early Oligocene time and from the northeast during
late Oligocene time.
Strontium isotope data from well 11/10–1, 9/12–1 and 2/2–2, analysed at the
University of Bergen. Sr ratios were corrected to NIST 987 = 0.710248. The numerical
ages were derived from the SIS look-up table version 3:10/99 of Howarth and McArthur
(1997). NIST – National Institute for
Standards and Technology.