Magne Formation (Magneformasjonen)
After Fritsen, A. & Riis, F. 2000. A revised chalk lithostratigraphic nomenclature; NPD Report, unpublished)
Chalk Group
Name
After the Norse god Magne, who was the son of Tor, and who supported him after his great fight with the giant Hrungnir (Sturluson, 1954).
Well type section
Well 1/3-8 4125-3952 m MD.
Well reference section
Well 2/11-A-2 T2, 3486-3427.4 m MD.
Thickness
The thickness of this formation ranges from zero to a few hundred metres in the study wells.
Lithology
Lithofacies associated with the crestal biofacies on the Valhall structure are typically (textural) mudstones
and wackestones. Those associated with the open marine platform, high productivity upper slope and
basinal biofacies are typically bioturbated argillaceous wackestones and chalks or interbedded chalks
and claystones (sometimes referred to as periodites), indicative of slow sedimentation or, in the case
of the basinal biofacies, incipient hardgrounds, indicative of extremely slow sedimentation (sediment
starvation). Those associated with the eutrophic sub-biofacies are bioturbated, those associated with
the dysoxic sub-biofacies are laminated (i.e., non-bioturbated) pyritic chalks.
Characteristics of the lower boundary
Picked primarily on a seismic criterion (onlap surface).
Characteristics of the upper boundary
Picked on seismic, biostratigraphic and log criteria. The seismic criterion is a reflector (which may also
locally be an onlap surface) separating a lower amplitude interval below from a higher amplitude interval
above, at least in structurally higher areas. The biostratigraphic criterion is penetration of microzone FCS21.
The log criterion is a downhole gamma increase (the Magne is more clay-rich than the overlying
Tor).
Geographical distribution
It is absent in the 31/26A-10 well in the United Kingdom Sector, thin (typically less than 100 m thick) on
structural highs such as Valhall-Hod, Eldfisk and Tor in the Norwegian Sector, and thickest in wells in
basinal lows such as those in the 1/3 and, locally, 2/5 areas in the Norwegian Sector.
Occurrences of formation tops in wells
Isochore map THUD-MAGNE
Biostratigraphy and Stage/Age
Late Early to early Late Campanian (for practical purposes, Campanian). Microzones intraFCS20pp-intraFCS22;
nannozones intraUC14pp-intraUC16pp. The base is taken near 81 Ma, using the criterion of 40% up in UC14.
