ØRRET FM

hide details Export:  PDF

• General information

  General information

  Attribute	Value
  Lithostrat. unit The lithostratigraphic unit's official name.	ØRRET FM
  NPDID lithostrat. unit Norwegian Offshore Directorate's unique id for lithostratigraphic units.	196
  Level Indicates the lithostratigraphic unit's level. Legal values: GROUP, FORMATION, MEMBER.	FORMATION
  Lithostrat. unit, parent The parent lithostratigraphic unit's official name. See also level. Will be empty if Level = GROUP.	TEMPELFJORDEN GP

• Level below

  Level below

  Lithostrat. unit

• Description

  Ørret Formation
  
  Name

  From the Norwegian name for the Brown Trout (Salmo trutta).

  Definition

  The type section is defined as the interval from 3670 m to 3475 m in 7124/3-1 on the Bjarmeland Platform (Fig 9.62) , Table 9.1). The base of the formation is characterised by a sharp increase in gamma ray log response accompanied by increasing neutron and sonic log readings in the type section where the formation overlies silicified limestones of the Røye Formation (Fig 9.62) .

  Reference sections

  Reference sections are defined:
  In Loppa well 7120/1-1 R with base at 2604 m, interfingering with a typical Røye development from 2458 m to 2430 and again overlain by the Røye Formation until the contact with overlying Triassic shales at 2402 m (Fig 9.51 , 9.55), from 3966 m to 3884 m in 7228/9-1 S on the northern margins of the Finnmark Platform (Fig 9.57) . As in the type section, the base of the formation is defined by a sharp increase in gamma ray log response accompanied by increasing neutron and sonic log readings in reference well 7228/9-1 S (and in 7229/11-1 ) on the northern Finnmark Platform, where the formation also overlies silicified sediments of the Røye Formation (Fig 9.51 , 5.33) .

  Thickness

  The formation is 195 m thick in the type well and has an aggregate thickness of 173 m in 7120/1-1 R on the Loppa High, whereas it is interpreted as not being developed in nearby well 7120/1-1 R . On the northern Finnmark Platform it is 82 m thick in well 7228/9-1 S , only 22 m in 7229/11-1 (Fig 9.51) , and disappears northwards so that wells 7128/4-1 and 7128/6-1 and cores 7128/12-U-01 and 7129/10-U-01 on the central and southern Finnmark Platform show only the Røye Formation directly overlain by Triassic shales. Tentative interpretations on the southern margins of the Hammerfest Basin in wells 7120/12-2 and 7120/12-4 suggest cumulative thicknesses of 656-901 metres.

  Lithology

  The formation is dominated by siliciclastic sediments and includes sandstones, siltstones and shales. The more fine-grained lithologies dominate. The sandstones (Fig 9.62) , appear as isolated thin beds, or as up to 35 m thick sandy units, or in intervals with numerous thin sandstone beds separated by shales. The sandstones are particularly common in the upper part of the Ørret Formation in 7120/12-2 (Fig 9.58) , and 7120/12-4 . On the Loppa High and further eastward, organic rich shales become progressively more important. Coal fragments are reported from some levels in association with sandstones. The siliciclastics are, in contrast to those of the Røye Formation , not silicified. Thin limestone beds are rare in the formation.

  Lateral extent and variation

  The formation is thickest in the deeper basinal and outer ramp areas of the Hammerfest Basin and the Finnmark and Bjarmeland platforms. Updip on the Finnmark Platform and the Loppa High it passes into the shallow marine carbonates of the Røye Formation . The transition from thin and organic-rich shales with rare thin sandstone and limestone beds in the east ( 7124/3-1 , 7226/11-1 , 7228/9-1 S and 7229/11-1 ) to thicker, more silty and sandy and less organic-rich lithofacies in wells 7120/12-2 and 7120/12-4 in the southwestern Hammerfest Basin and Finnmark Platform, suggests a southwesterly-located siliciclastic provenance area. In these southwestern wells, where the formation is thought to interfinger with the Røye Formation , the basal transition is always characterised by a sharp increase in gamma ray log response reflecting the transition from silicified carbonates to fine-grained non-silicified siliciclastics (Fig 9.58 , 9.62) .

  Age

  A ?Kungurian to ?Tatarian age is suggested by correlation to lateral equivalents.

  Depositional environments

  Deposition took place in a variety of siliciclastic-dominated environments ranging from deltaic and lower coastal plain environments in the southwestern Hammerfest Basin to deep shelf environments on the southern Bjarmeland Platform and the northern Finnmark Platform. Dysoxic to anoxic conditions occurred locally in the deeper shelf settings to the east.

  Source

  • Larssen, G. B., Elvebakk, G., Henriksen, L. B., Kristensen, S. E., Nilsson, I., Samuelsberg, T. J., Svånå, T. A., Stemmerik, L. and Worsley, D. 2002: Upper Palaeozoic lithostratigraphy of the Southern Norwegian Barents Sea. NPD-Bulletin No. 9, 69 pp.

• Wellbores penetrating

  Wellbores penetrating

  Wellbore name	Wellbore completion date	Top depth [m]	Bottom depth [m]
  7120/1-1	15.11.1985	2403	2430
  7120/1-1	15.11.1985	2458	2569
  7120/1-1 R	26.12.1985	2403	2430
  7120/1-1 R	26.12.1985	2458	2604
  7120/1-1 R2	21.07.1986	2403	2430
  7120/1-1 R2	21.07.1986	2458	2604
  7120/12-2	11.09.1981	3657	3920
  7120/12-2	11.09.1981	3975	4031
  7120/12-2	11.09.1981	4076	4485
  7120/12-4	16.04.1984	1366	1469
  7120/12-4	16.04.1984	1502	1648
  7120/12-4	16.04.1984	1688	1700
  7120/12-4	16.04.1984	1728	2003
  7124/3-1	20.10.1987	3475	3670
  7132/2-2	07.04.2019	3405	3454
  7225/3-1	25.09.2011	3666	3771
  7226/11-1	11.04.1988	3877	3966
  7228/9-1 S	07.05.1990	3884	3966
  7229/11-1	15.12.1993	3879	3901
  7234/6-1	19.07.2021	3711	3758
  7322/6-1 S	28.05.2021	2519	3094

• Wellbores with cores

  Wellbores with cores

  Wellbore name	Wellbore completion date	Core length [m]
  7120/12-2	11.09.1981	28
  7120/12-4	16.04.1984	18