GASSUM FM

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• General information

  General information

  Attribute	Value
  Lithostrat. unit The lithostratigraphic unit's official name.	GASSUM FM
  NPDID lithostrat. unit Norwegian Offshore Directorate's unique id for lithostratigraphic units.	49
  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.

• Level below

  Level below

  Lithostrat. unit

• Description

  Gassum Formation
  
  Name

  After the village of Gassum, Jutland, Denmark, (Larsen, 1966).

  Well type section

  Danish well Gassum No. 1 from 1613 m to 1643 m below ground (Ground evelation 53.3 m) (Bertelsen, 1978).

  Well reference sections

  In Norwegian waters wells 17/10-1 (Shell) from2682 m to 2825 m, coord N 58°01 '54", E 03°09'58" (Fig 3.23) . and 7/9-1 (Conoco) from 2601 m to 2609 m, coord N 57°20' 37.1", E 02°51'21.4" (Fig 3.24) . The section in well 17/10-1 was included by Deegan and Scull (1977) in the Skagerrak Formation .

  Thickness

  In the Norwegian reference wells the thickness of the Gassum Formation is 143 m ( 17/10-1 ) and 8 m ( 7/9-1 ).

  Lithology

  In the type well the formation consists of predominantly light grey to whitish, in places rather coarse-grained sandstones, with subordinate dark-coloured clay bands and coal lenses (Larsen, 1966). In Norwegian waters the formation is predominantly a white to light grey, mainly fine to medium grained sandstone, but frequently contains coarse sand and gravel. It is often calcite cemented and in some instances contains glauconite.

  Boundaries

  In the Norwegian sector the lower boundary may be characterized by a general lowering of the velocity when entering the underlying Skagerrak Formation . Often this boundary coincides with a distinct horizon with high gamma ray response (e.g. well 17/4-1 (Elf) and well 9/12-1 (Shell)).
  The upper boundary of the Gassum Formation is easily picked where it is overlain by Lower Jurassic shales of the Fjerritslev Formation or Upper Jurassic shales of the Boknfjord or Tyne groups. Where the Gassum Formation is overlain by the Middle Jurassic Bryne Formation (Norwegian sector), the boundary may only show a slight decrease in the gamma ray response and an overall decrease in velocity marking the appearance of the Bryne Formation .
  In the reference well 17/10-1 , where the Fjerritslev and Bryne formations are missing, the Gassum Formation is overlain by the shales of the Boknfjord Group .

  Distribution

  In the Norwegian sector the Gassum Formation occurs throughout the Norwegian-Danish Basin, on the Southern Vestland Arch and along the northeastern margin of the Central Graben. Its distribution towards the axial part of the Central Graben is unknown. It is often completely or partially eroded as a result of mid-Jurassic earth movements.

  Age

  Rhaetian in the type well, but seems to become younger northwards (Bertelsen, 1978). Sparse dating in the Norwegian sector gives Rhaetian to Sinemurian ages.

  Depositional environment

  The sedimentology of the Gassum Formation in the Norwegian sector has not been much studied, but is assumed to represent fluvial to marginal marine deposits laid down during a transgressive phase at the Triassic/Jurassic transition.

  Source

  • Vollset, J. and Doré, A. G. (eds.) 1984: A revised Triassic and Jurassic lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No. 3, 53 pp.

• Wellbores penetrating

  Wellbores penetrating

  Wellbore name	Wellbore completion date	Top depth [m]	Bottom depth [m]
  3/5-2	20.08.1978	3575	3604
  7/8-1	05.02.1969	3275	3334
  7/9-1	29.05.1971	2601	2609
  7/12-2	23.09.1976	3554	3676
  8/1-1	07.02.1972	2680	2704
  9/11-1	19.08.1971	2082	2121
  10/5-1	26.06.1976	1524	1539
  10/8-1	17.01.1971	1494	1567
  11/10-1	19.08.1969	1860	1900
  17/6-1	07.02.2011	2800	2988
  17/8-1	23.10.2021	2455	2466
  17/10-1	24.03.1969	2682	2825
  17/12-1 R	21.06.1972	2410	2446
  17/12-3	03.02.1980	2617	2638

• Wellbores with cores

  Wellbores with cores

  Wellbore name	Wellbore completion date	Core length [m]
  7/12-2	23.09.1976	18