Upper Miocene to Lower Pliocene
T. Eidvin, F. Riis, E. S. Rasmussen & Y. Rundberg, 2013. New layout 2021
East Greenland, off Scoresby Sund
The lithology at ODP Site 987 (Map 2) principally consists of silty clay with varying amounts of ice-rafted clasts and stones. The succession is seen to consist of three dominantly hemipelagic sections with varying input from ice rafting (Units I, III and IV in Butt et al. 2001) and two debris flow units (Units II and IV in Butt et al. 2001). We have not investigated samples from Units I and II. The existence of ice on continental Greenland is indicated since approximately 7.5 Ma (Unit V), but the depositional environments at this time were dominantly hemipelagic. The first major advance across the Scoresby Sund took place at approximately 5 Ma (Unit IV). A return to a dominantly hemipelagic environment took place at around 4.5 Ma (Unit III). Another major glacial advance across the shelf at 2.58 Ma is represented by another debris flow unit (Unit II). This phase is related to the onset of major Northern Hemisphere glaciations at approximately 2.6 Ma (Butt et al. 2001, Laberg et al. in press).
Larsen (1990) identified 12 seismic sequences along line GGU 82-12 where the deposits reach a thickness of over 3 km on the outer shelf (see Profile P14). The earliest sedimentation was dated to Eocene to Early Oligocene (sequences 1-2) and the major sedimentation phase (sequences 3-8) to Miocene. The uppermost units 9-12 were interpreted as representing Plio-Pleistocene deposition. Site ODP 987 was drilled on the eastern extremity of the GGU 82-12 line (Profile 14). The age model for Site 987 suggests that although sedimentation may have started during Late Miocene times, the section is dominated by Plio-Pleistocene deposits (ODP Site 987, Fig. 1, Channel et al. 1999, Butt et al. 2001).
Barents Sea – Svalbard
In the Barents Sea shelf, Upper Miocene sediments are only preserved in a distal position in local basins along the western margin (well 7216/11-1 S, Ryseth et al. 2003). In northern Spitsbergen, a sequence of volcanic rocks overlying crystalline basement and Devonian sediments has been tentatively dated to Late Miocene (Vågnes & Amundsen 1993).
Norwegian Sea and its continental shelf
A marked relief of the Fennoscandian Shield, accompanied by continued uplift, colder climate (Fig. 5) and a low global sea-level, resulted in a continued and pronounced out-building of the coastal plains and deltas along the inner continental shelf (Molo Formation). Upper Miocene to Lower Pliocene deposits are recorded from the Molo Formation in well 6407/9-5, 6407/9-1 and 6407/9-2 in the Draugen Field in its southwestern part (Map 1, Fig. 1). In these wells the Molo Formation contains glauconitic sand. There is not sufficient data to determine whether there is a hiatus between the Lower Miocene and the Upper Miocene-Lower Pliocene part of the formation (Fig. 5).
Sediments belonging to the Kai Formation were deposited on the outer and middle parts of the margin. On the outer shelf and slope down to the deeper Møre and Vøring basins, the Kai Formation is overall clayey (e.g. wells 6607/5-1, 6609/5-1, 6508/5-1, 6609/11-1 and 6507/12-1) with ooze in the basinal part (e.g. boreholes 6704/12-GB1 and 6403/5-GB1 and well 6305/5-1, Map 1, see also figure 9c in Henriksen et al. 2005). It has a similar polygonal fault pattern as the Brygge Formation, although in detail there are differences in seismic facies between the two units (Bugge et al. 2004, Eidvin et al. 2007). According to Laberg et al. (2005a, 2005b) and Henriksen et al. (2005), in the Norwegian Sea the sediments of the Kai Formation have to a large extent been redistributed by contour currents. At this time, the sea-floor bathymetry was controlled by large domes and depressions formed by the Mid Miocene compressional tectonic phase. Seismic data indicate that redistribution of fine-grained sediments commonly took place along the flanks of the domes. Fig. 13 shows the redistribution of Miocene sediments in a section through the Sør High, a part of the Nordland Ridge which underwent Mid Miocene compression.
Northern and central North Sea
During the Late Miocene to Early Pliocene, the northern North Sea formed a narrow seaway between deeper water in the Møre Basin and the central North Sea. The strait received large amounts of coarse sand (Utsira Formation). The Utsira Formation represents a huge sedimentary depositional system in the northern North Sea (about 450 km long and 90 km wide, Fig. 11) comprising one large sandy depocentre (250-300 m in the southern Viking Graben) and an area with 80-100 m-thick sandy deposits in the northern Viking Graben. The western central area comprises a large deltaic system which prograded eastwards in the Early and Mid Miocene, but where Upper Miocene to Lower Pliocene sediments of the Utsira Formation are thin or absent (Fig. 3). Apparently, the progradation of the delta stopped in the Mid/Late Miocene, and the sediments were transported to the delta slope and the shallow shelf beyond the delta, suggesting a relative fall in sea level. To the north, in the Tampen area, the Utsira Formation is represented by a thin glauconitic unit dated to close to the Late Miocene/Early Pliocene boundary and overlying the Oligocene and Lower Miocene. This member is thought to cap the main Utsira Formation sands in the northeastern part of the basin (Fig. 11, Profile P8, Rundberg & Eidvin 2005, Eidvin & Rundberg 2001 and 2007). Within the Tampen area, the glauconitic member is locally absent and Upper Pliocene deposits lie unconformably on Oligocene sediments, e.g. in the Tordis Field area (Eidvin 2009 and Eidvin & Øverland 2009). In the western part of the Norwegian sector in quadrants 30 and 25, the Utsira Formation merges with parts of the Hutton sand (see Profile P6). Offshore West Norway, a sandy deltaic system was developed north of the Troll Field, probably fed by the Sognefjorden paleovalley (Map 1, Profile P8). Farther to the south, only thin and shaly sections are recorded.
Northern Central Graben
In the Ekofisk area, the Upper Miocene to Lower Pliocene succession has been investigated in well 2/4-C-11 (Map 1) and contains mostly clay. Seismic data show a parallel to sub-parallel, rather continuous, reflection pattern. The section thickens into the Central Graben depocentre, but there are no clear indications of any direction of progradation. At its base, a faint onlap has been observed along the lower boundary at the Mid Miocene reflector. In the Ekofisk area, the section may be tentatively divided into a lower part with more continuous internal reflections and an upper part with less continuity. This change takes place within the Upper Miocene. The upper part seems to onlap the lower section towards the north (Eidvin et al. 1999). The Lower Pliocene succession is characterised by a low-angle, northward-dipping, clinoformal reflection pattern. Locally, pockmarks characterise the Pliocene succession (Knutz 2010).
At the lower boundary of the interval, the base Upper Miocene reflector is well defined by a conspicuous change in internal deformation, the underlying unit being strongly polygonally faulted. From regional mapping, it is known that the base Upper Miocene reflector commonly defines the top of gas chimneys and that it coincides with the latest phase of major salt movement in the Central Graben. Pressure build-up above hydrostatic is commonly encountered below the reflector/unconformity. Above the big, chalk, oil and gas fields, gas chimneys and undercompacted clays are also encountered in the Upper Miocene and Lower Pliocene succession (Eidvin et al. 1999).
Norwegian-Danish Basin
Onshore Denmark, the base of the Upper Miocene is characterised by a regional oxidation of glauconite minerals to goethite (Map 1 and Link to Danish Miocene Sr isotope ages). This reflects a relative sea-level fall in the area (Rasmussen 2004). The sedimentation during the Late Miocene was dominated by deposition of clay-rich sediments with an increasing incursion of sand in the upper part. The thin sand beds were deposited as storm sand layers, but show a clear tidal influence, i.e. with double clay drapes. In the latest Late Miocene, shoreface deposits were laid down in the Danish area and the shoreline prograded as far as the Central Graben at the end of the Late Miocene (Rasmussen 2005, Møller et al. 2009).