Lower Pliocene dinoflagellate cysts from cored Utsira Formation in the Viking Graben, northern North Sea

Abstract The Utsira Formation covers an area of at least 75×450 km 2 with its main, sandy depocentre in the southern Norwegian Viking Graben. Here in the Sleipner area, the formation is c. 300 m thick and pinches out to the west, south and east. It consists of unconsolidated, very fine- to medium-grained sand mainly composed of quartz with small amounts of glaucony, shell fragments and lignite, probably deposited by turbidite flows. Earlier biostratigraphical studies of the Utsira Formation have been based on cuttings and the age has been considered to be mainly Late Miocene potentially including latest Middle Miocene and earliest Pliocene. In the present study, core samples from the well 15/9-A23 situated in the Sleipner area have been studied. Dinoflagellate cysts were prepared from seven samples of very fine- to fine-grained sand taken from a core in the interval of 1080.0–1084.99 m. A mixture of Middle and Upper Miocene stratigraphic marker-species indicate significant reworking of older species into younger strata. The main stratigraphical problem is therefore to distinguish reworked species from the in situ flora. The presumed in situ dinoflagellate flora comprises overall Upper Miocene to Pliocene species with relatively few species of precise and clear stratigraphical significance. A single record of Selenopemphix armageddonensis in the lowest sample suggests top Miocene or younger strata. Several dinoflagellate cysts in the assemblage are well known from the Pliocene or even the Pleistocene of the North Atlantic region. Some acritarchs are particularly characteristic of the Pliocene of the northern North Atlantic region. This age is supported by the presence of species such as Hystrichokolpoma rigaudiae and Reticulatosphaera actinocoronata which are reported to range into the Lower Pliocene in the northern North Atlantic region. But the youngest possible age of these samples based on the content of dinoflagellate cysts is strongly dependent on the interpretation of which species that are considered reworked. However Amiculosphaera umbracula , Invertocysta lacrymosa and Ataxiodinium zevenboomii are generally reported to reach stratigraphically not much higher than mid-Pliocene. The age of the cored interval of the Utsira Formation is therefore considered to be Early Pliocene, and this makes a significant part of the formation younger than indicated by previously published biostratigraphic data.

[1]  Peter Japsen,et al.  Neogene uplift and tectonics around the North Atlantic: overview , 2000 .

[2]  P. Mudie,et al.  Palynology and Dinocyst Stratigraphy of the Miocene in ODP Leg 105, Hole 645E, Baffin Bay , 1989 .

[3]  S. Louwye,et al.  Dinoflagellate cysts of the shallow marine Neogene succession in the Kalmthout well, Northern Belgium , 1998 .

[4]  Martin B. Farley,et al.  Mesozoic and Cenozoic Sequence Chronostratigraphic Framework of European Basins , 1998 .

[5]  E. Jansen,et al.  The upper Cainozoic of the Norwegian continental shelf correlated with the deep sea record of the Norwegian Sea and the North Atlantic , 2000 .

[6]  D. Evans,et al.  The millennium atlas : petroleum geology of the central and northern North Sea , 2003 .

[7]  A. Powell.  A Stratigraphic index of dinoflagellate cysts , 1992 .

[8]  M. Smelror.  6. PLIOCENE-PLEISTOCENE AND REDEPOSITED DINOFLAGELLATE CYSTS FROM THE WESTERN SVALBARD MARGIN (SITE 986): BIOSTRATIGRAPHY, PALEOENVIRONMENTS, AND SEDIMENT PROVENANCE 1 , 1999 .

[9]  S. B. Banum.  Dinocysts in Tertiary Norwegian-Greenland Sea Sediments (Deep Sea Drilling Project Leg 38) with Observations on Palynomorphs and Palynodebris in Relation to Environment , 1976 .

[10]  W. E. Galloway,et al.  Sequence stratigraphic and depositional framework of the Cenozoic fill, Central and Northern North Sea Basin , 1993 .

[11]  F. Riis.  Quantification of Cenozoic vertical movements of Scandinavia by correlation of morphological surfaces with offshore data , 1996 .

[12]  F. Riis,et al.  Upper Cainozoic stratigraphy in the central North Sea (Ekofisk and Sleipner fields) , 1999 .

[13]  R. Fensome,et al.  The stratigraphic importance of species of Sumatradinium, Barssidinium, and Erymnodinium, Neogene dinoflagellate genera from offshore eastern Canada , 1994 .

[14]  G. Williams,et al.  Tertiary dinoflagellate biostratigraphy of Sites 907, 908, and 909 in the Norwegian-Greenland Sea , 1996 .

[15]  M. Head.  Thermophilic dinoflagellate assemblages from the mid Pliocene of eastern England , 1997, Journal of Paleontology.

[16]  F. Riis,et al.  On the magnitude of the Late Tertiary and Quaternary erosion and its significance for the uplift of Scandinavia and the Barents Sea. , 1992 .

[17]  Olaf Michelsen,et al.  Stratigraphy and facies distribution of the Utsira formation and the Pliocene sequences in the northern North Sea , 1997 .

[18]  S. Louwye.  New species of organic-walled dinoflagellates and acritarchs from the Upper Miocene Diest Formation, northern Belgium (southern North Sea Basin) , 1999 .

[19]  P. Mudie,et al.  Palynology and Dinocyst Stratigraphy of the Upper Miocene and Lowermost Pliocene, ODP Leg 105, Site 646, Labrador Sea , 1989 .

[20]  H. Gunnarsdóttir,et al.  Eocene to Miocene Palynology of the Norwegian Sea (ODP Leg 104) , 1989 .

[21]  J. Faleide,et al.  Cenozoic sequence stratigraphy of the central and northern North Sea Basin: tectonic development, sediment distribution and provenance areas , 1995 .

[22]  S. Ghazi.  Cenozoic uplift in the Stord Basin area and its consequences for exploration , 1992 .

[23]  O. Martinsen,et al.  Cenozoic development of the Norwegian margin 60–64°N: sequences and sedimentary response to variable basin physiography and tectonic setting , 1999 .

[24]  L. Edwards.  Miocene Dinocysts from Deep Sea Drilling Project Leg 81, Rockall Plateau, Eastern North Atlantic Ocean , 1984 .

[25]  A. Powell.  Dinoflagellate cysts of the Tertiary System , 1992 .

[26]  A. Vernal,et al.  Late Pliocene to Holocene Palynostratigraphy at ODP Site 645, Baffin Bay , 1989 .

[27]  G. Norris,et al.  Miocene Dinoflagellate Stratigraphy and Systematics of Maryland and Virginia , 1996 .