Reply to comment of P. Japsen et al. on “Cenozoic evolution of the eastern Danish North Sea” (original) (raw)
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Cenozoic evolution of the eastern Danish North Sea
Marine Geology, 2001
This paper provides a review of recent high-resolution and conventional seismic investigations in the eastern Danish North Sea and describes their implications for the development of the eastern North Sea Basin. The results comprise detailed timestructure maps of four major unconformities in the eastern Danish North Sea: the Top Chalk surface (mid-Paleocene), near top Oligocene, the mid-Miocene unconformity, and base Quaternary. The maps show that the eastern Danish North Sea has been affected by faulting and salt diapirism throughout the Cenozoic. Carbonate mounds, erosional valleys and pockmark-or karstlike structures were identi®ed at the top of the Upper Cretaceous±Danian Chalk Group.
Marine and Petroleum Geology, 1997
ELSEVIER .2fu~im~ t/m/ Pctu~/cum G'eolq>~. Vol. 14. No. 7,X. pp. 93 I 950. lYY7 m( Five sequences are defined in the Oligocene succession of the Danish North Sea sector. Two of the sequences, 4.la and 4.3, have been identified onshore Denmark. Two types of prograding lowstand deposits are recognized. Sand-dominated deposits occur proximally, comprising sharp-based forced regressive deposits covered with prograding lowstand deposits. Clay-dominated prograding lowstand deposits occur distally in the sequences. The highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals. The main sediment input direction was from the north and the northeast. A succession of lithofacies, from shallow marine facies dominated by sand to outer shelf facies dominated by clay, is mapped in each of the sequences. An overall southward progradation of the shoreline took place during the Oligocene, interrupted only by minor shoreline retreats. 0 1998 Elsevier Science Ltd. All rights reserved Tel: +45 X9 42 25 17; fax: +45 X6 13 91 4X; r-mail: geolmdwaau.dk 153-175. Christensen, L. and Ulleberg, K. (1973) Sedimentology and micropalaeontology of the Middle Oligocene Viborn Formation. Bulletin of the Danish Geological Society 22, 283-305. Clausen 0. Ft., Korstnbrd J. A. (1993) Tertiarv tectonic evolution along the Arne-Eli Trend in the Danish Central Trough. Terra Nova 5,233-243. Danielsen, M. (1989) En sedimentologisk undersogelse afTerti%re
Geological Society, London, Special Publications, 2012
Despite a long history of investigation, several critical issues regarding the glacial history of 11 Northwest Europe, particularly in currently marine areas, remain unsolved. In this study we 12 present a comprehensive 3D seismic interpretation of an area of 2,000 km² in the western 13 part of the Danish North Sea that exhibits several buried, Quaternary landforms. Well data 14 are used to assign minimum and maximum ages for the studied sedimentary succession.
Mid-Paleocene palaeogeography of the Danish area
At the Danian/Selandian transition the North Sea Basin experienced a marked change, from deposition of almost pure carbonate during the Upper Cretaceous and Danian to deposition of greensand, marl and clay during the Selandian. Erosional features at the Top Chalk surface and the occurrence of an overlying conglomerate (transgressive lag deposit) indicates that large parts of the Danish area were subaerially exposed at the Danian/Selandian transition, probably due to regional tectonic uplift. Tectonically induced inversion of fault trends in the Central Trough and the Sorgenfrei-Tornquist Zone and differential relative subsidence between the Ringkøbing-Fyn High and the Norwegian-Danish Basin strongly affected the distribution of the lower Selandian sediments. Three palaeogeographic maps are presented to illustrate the various stages of the early Selandian transgression in order to demonstrate the mid-Paleocene evolution of the Danish area.
Marine and Petroleum Geology, 2009
A large-scale enigmatic mound structure (M1) has been discovered in middle Miocene strata of the Norwegian-Danish Basin, c. 10 km east and updip of the Central Graben. It is located about 1 km beneath the seabed and clearly resolved by a 3D seismic data set focused on the deeper, remobilised, sand-filled Siri Canyon. M1 comprises two culminations, up to 80 m high and up to 1400 m long, constituting a sediment volume of some 5.3 Â 10 7 m 3 . It is characterized by a hard reflection at the top, a soft reflection at the base, differential compaction relative to the surrounding sediments, and 10 ms TWT velocity pull up of underlying reflections, indicating a relatively fast mound fill, attributed to the presence of sand within the mound. Internal seismic reflections are arranged in an asymmetric concentric pattern, suggesting a progressive aggradation to the NW, downstream to a mid-Miocene contour current system. Numerous elongated pockmarks occur in the upper Miocene succession close to the mound and indicate that the study area was influenced by gas expulsion in the mid-and late Miocene. The reflection configuration, velocity, dimensions, regional setting, and isolated location can best be explained by interpreting the mound as a giant sand volcano extruded >1 km upward from the Siri Canyon during the middle Miocene (c. 15 Ma). The likely causes of this remarkable structure include gas charge and lateral pressure transfer from the Central Graben along the Siri Canyon reservoir. While this is the first such structure described from this part of the North Sea, similar-aged sand extrudites have recently been inferred from seismic observations in the North Viking Graben, thus suggesting that the mid-Miocene was a time of widespread and intense sediment remobilization and fluid expulsion in the North Sea.
Norwegian Journal of Geology
The almost complete, mainly deltaic, upper Paleogene and Neogene succession in Jylland, Denmark, was previously investigated for 87Sr/86Sr ratios in 143 samples from 18 localities. In the present paper, strontium-isotope data from the Upper Oligocene-Lower Miocene parts and foraminiferal and pyritised diatoms data from 94 of these samples were used to correlate with previously published data from Norwegian wells and boreholes and one borehole in the British sector of the North Sea. For the Middle-Upper Miocene parts of the succession the correlation is based mainly on Bolboforma data. The ages of the geological formations in the Danish succession correlate readily with lithological units in the Norwegian North Sea, the Norwegian Sea shelf and the East Shetland Platform, which have all been investigated applying similar methods. The Bolboforma assemblages have their origin in the North Atlantic and the Norwegian Sea and confirm the presence of an open strait in the northern North Sea. This strait was the only seaway passage into the North Sea Basin during the Miocene. The glauconitic Utsira Formation sand (approximately 5.7-4.2 Ma), in the threshold area close to the outlet to the Norwegian Sea, overlies erosional unconformities comprising hiati of 21 my in some areas and 13 my in other areas. We believe that the unconformity below the Utsira Formation was mainly related to a fall in sea level in the Late Miocene, contemporaneous with that partly responsible for the Messinian salinity crisis. Bolboforma and dinoflagellate cysts stratigraphy indicate that the base of the Molo Formation in its southern distribution area (Draugen Field, Trøndelag Platform) is of Late Miocene age (close to 9 Ma). This part of the Molo Formation was contemporaneous with the middle/upper part of the Kai Formation.
Basin Research, 2007
Four Mesozoic^Cenozoic palaeothermal episodes related to deeper burial and subsequent exhumation and one re£ecting climate change during the Eocene have been identi¢ed in a study of new apatite ¢ssion-track analysis (AFTA s ) and vitrinite re£ectance data in eight Danish wells.The study combined thermal-history reconstruction with exhumation studies based on palaeoburial data (sonic velocities) and stratigraphic and seismic data. Mid-Jurassic exhumation (ca. 175 Ma) was caused by regional doming of the North Sea area, broadly contemporaneous with deep exhumation in Scandinavia. A palaeogeothermal gradient of 45 1C km À 1 at that time may be related to a mantle plume rising before rifting in the North Sea. Mid-Cretaceous exhumation a¡ecting the Sorgenfrei^Tornquist Zone is probably related to late Albian tectonic movements (ca.100 Ma).The Sole Pit axis in the southern North Sea experienced similar inversion and this suggests a plate-scale response along crustal weakness zones across NW Europe. Mid-Cenozoic exhumation a¡ected the eastern North Sea Basin and the onset of this event correlates with a latest Oligocene unconformity (ca. 24 Ma), which indicates a major Scandinavian uplift phase.The deeper burial that caused the late Oligocene thermal event recognized in the AFTA data re£ect progradation of lower Oligocene wedges derived from the uplifting Scandinavian landmass.The onset of Scandinavian uplift is represented by an earliest Oligocene unconformity (ca. 33 Ma). Late Neogene exhumation a¡ected the eastern (and western) North Sea Basin including Scandinavia.The sedimentation pattern in the central North Sea Basin shows that this phase began in the early Pliocene (ca. 4 Ma), in good agreement with the AFTA data. These three phases of Cenozoic uplift of Scandinavia also a¡ected the NE Atlantic margin, whereas an intra-Miocene unconformity (ca.15 Ma) on the NE Atlantic margin re£ects tectonic movements of only minor amplitude in that area.The study demonstrates that only by considering episodic exhumation as an inherent aspect of the sedimentary record can the tectonic evolution be accurately reconstructed.
Upper Cainozoic stratigraphy in the central North Sea (Ekofisk and Sleipner fields)
Norsk Geologisk Tidsskrift, 1999
The investigation is based on analyses of planktonic and benthonic forarninifera and Bo/boforma carried out in the uppermost Palaeogene and Neogene of the production well 2/4-C-11 (56°33' N, 3°13' E) on the Ekofisk Field and the exploration well 15/12-3 (58°14' N, 1"53' E) on the Sleipner Field. The analyses are based primarily on ditch cuttings, but in we11 2J4-C-ll, 49 sidewall cores and six short conventional cores were also available. Strontium isotope and paleomagnetic analyses were also carried out in well 2/4-C-11. A 420 m-thick accumulation of Lower Miocene sediments is present in the Ekofisk area. The Middle Miocene comprises approximately 180m, and the Upper Miocene is represented by an approximately 500 m-thick interval. A hiatus is present in the Middle Miocene, and the middle part of the Middle Miocene is missing. A !hin interval (approximately 120m) of Lower Pliocene sediments is found overlying the Upper Miocene. Uppermost, a thick accumulation of Upper Pliocene-Pleistocene sediments (approximately 1000 m) is in place. More !han half of !his was deposited during the Pleistocene. The entire Upper Pliocene is represented in this area. This contrasts to the northem North Sea, as well as areas further north, where sediments of !his epoch are partially missing in a hiatus comprising the lowermost part of the Upper Pliocene. In the Sleipner area the Lower and Middle Miocene are approximately 160m and 180m thick, respectively. The Upper Miocene (approximately 100 m) and the Lower Pliocene (approximately 40 m) !hin from the Ekofisk towards the Sleipner Field. Uppermost, an approximately 900 m-thick succession of Upper Pliocene-Pleistocene sediments is present. Nearly two-thirds of this accumulation are Pleistocene in age.
Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64 N-68 N
Norsk Geologisk Tidsskrift, 1998
This investigation is based on six exploration wells: 6607/5-1 and /5-2 (Utgard High), 6506/1 2-4 (Halten Terrace), 6610/7-1, 6610/7-2 and 6610/3-1 (Nordland Ridge). Fifteen inforrnal fa una zones are outlined. Thick, glacially derived Pleistocene and Upper Pliocene prograding shelf deposits extend along the continental margin of the Norwegian Sea. In well 6607/5-1 and 6506/1 2-4 Upper Pliocene outer to middle shelf deposits Iie unconforrnably on Upper Miocene outer shelf deposits, which are well developed in these areas. A thin interval of Middle Miocene outer shelf sediments is present in well 6607/5-1. This rests unconforrnably upon Lower/Middle Eocene middle to outer shelf deposits, which in turn rest unconforrnably upon the Upper Cretaceous. In well 6506/12-4, the Upper Miocene rests unconforrnably on outer to middle shelf sediments from the Upper Oligocene/Lower Miocene, which in turn Iie unconforrnably on the Lower/Middle Eocene. In well 6607/5-2 Upper Pliocene outer shelf sediments Iie unconforrnably on the Lower/Middle Eocene. Wells 6610/7-1 and /7-2 on the Nordland Ridge penetrate the proximal, oldest parts of the glacially derived prograding sediments of Late Pliocene age, which in this area are middle to inner shelf deposits. In addition, wells 6610/7-1 and 6610/3-1 penetrate underlying Early Oligocene coastal deposits. Lower/Middle Eocene sediments Iie below the coastal deposits in well 6610/7-1. In well 6610/7-2 Upper Pliocene deposits Iie unconforrnably upon low oxic deep basin sediments from the Upper Paleocene. Seismic profiles through this area show that the Upper Pliocene glacial deposits onlap the Lower Oligocene coastal deposits.