Spekk Formation (Spekkformasjonen)
(From NPD Bulletin no. 4)
Viking Group
Name
The Norwegian word for blubber. The unit corresponds to the
informal Nesna formation (H2-2).
Well type section
Well 6407/2-1
(Saga Petroleum), coordinates 64°58'04.97"N, 07°28'28.11"E, from 2908 m to
2842,5 m (Fig. 24).
Well reference section
Well 6407/9-1
(Shell), coordinates 64°21'55,39"N, 07°47'21.76"E, from 1673 m to 1612 m
(Fig. 22). This section includes 49 m of the
Rogn Formation. The lowermost
part, including the base is cored, but the atypical development of the
succession in the Draugen Field makes this well unsuitable as type
section.
Thickness
65,5 m in the type well, 14 m in the reference well.
Lithology
The formation consists of dark brown to dark grey shale. The shale is
predominantly noncalcareous. Parts of the unit may be silty. The organic
content (mainly of type II kerogen) is very high.
Basal Stratotype
The formation has a characteristic high gamma log response and the sonic
log shows high interval transit times. The base is defined by a sharp
increase in the gamma ray response and a drop in sonic log readings. High
velocity limestone stringers close to the base of the formation may
complicate the basal pick on the sonic log.
Lateral extent and variation
The formation was probably deposited throughout the
Haltenbanken-Trænabanken area, but may now be absent from the Nordland
Ridge and other structural highs. Unusually thick sections may be present
in structural lows.
Occurrences of formation tops in wells
Isochore map MELKE-SPEKK
Age
Oxfordian to Ryazanian.
Depositional environment
The unit's shales were deposited in marine
anoxic bottom water conditions.
Correlation
The Spekk Formation has a higher, more uniform gamma ray response than the
partially time equivalent Draupne Formation in
the northern North Sea. The
two formations are lithologically similar with dark claystones and high
organic contents. The Spekk Formation is time equivalent to the Hekkingen
Formation in the Hammerfest Basin.
