Network of Offshore Records of Geology and Stratigraphy

NORLEX

Draupne Formation (new)

Name

From a gold ring owned by Odin (the mythologic Viking God) which "dripped" 7 new rings, of the same weight as the original, every 9th day. The name is considered particularly appropriate in view of the Draupne Formation's role as a prolific hydrocarbon source in the Northern North Sea. It replaces the name "Kimmeridge Clay Formation" as used by Deegan and Scull (1977) in the Northern North Sea (see remarks).

Well type section

Norwegian well 30/6-5 (Norsk Hydro), from 2452 m to 2615 m, coord N 60°41'20.6", E 02°57'11.09", (Fig. 22).

Well reference sections

UK wells 211/21-1A (Shell), from 2729.5 m to 2810 m, coord N 61°ll'09.6" E 01°06'45", (Fig. 18), and 210/30-1 (Arpet), from 3330 m to 3717.5 m, coord N 61°04'05.4", E 00°54' 14.4'', (Fig. 20), and Norwegian wells 33/9-1 (Mobil) from 2443 m to 2450 m, coord N 61°15'07.5" E 01°50'25.8", (Fig. 11), 15/9-2 (Statoil) from 3397 m to 3478 m, coord. N 58°25'34.06" E 01°42'28.2", (fig. 26), and 15/3-1 (Elf) from 3947 m to 4754 m, coord N 58°50'57.00", E01°43'13.25", (Fig. 19).

Thickness

163 m in the type well, 80,5 m in 211/21-1 A, 387,5 m in 210/30-1, 7 m in 33/9-1, 81 m in 15/9-2, and 807 m in 15/3-1

Lithology

The formation consists of dark grey-brown to black, usually non-calcareous, carbonaceous, occasionally fissile claystone. It is characterized by very high radioactivity (often above 100 API units) which is a function of organic carbon content. It has anomalously low velocity, density and high resistivity. Minor limestone streaks and concretions occur throughout the formation. In addition interbedded sandstones and siltstones can cause a reduction in gamma ray response. The reference well 15/3-1 is an atypical example of the Draupne Formation which has been chosen to illustrate these arenaceous intercalations.

An informal three-fold subdivision has been identified, and is best recognizable along the basin rim areas where a middle high gamma ray zone separates two zones of lower gamma ray response (e.g. 210/30-1).

Boundaries

These are marked by distinct log breaks due to the very high gamma ray response and low velocity shown by the Draupne Formation.

In basinal areas the formation generally has a diachronous contact with the Heather Formation. On marginal highs the formation onlaps pre-Upper Jurassic rocks. On the northern Horda Platform, Upper Jurassic sandstones of the Sognefjord Formation mark the base of the Draupne Formation.

The upper boundary is often an unconformity or discontinuity, usually overlain by Cretaceous sediments which have a higher velocity and lower gamma ray response than the Draupne Formation. The importance and regional validity of this unconformity is currently under debate; see for example Rawson and Riley (1982).

Distribution

The formation is found in the East Shetland Basin, the Viking Graben and over the Horda Platform.

Occurrences of formation tops in wells

Age

The formation ranges from Oxfordian to Ryazanian in age.

Depositional environment

The Draupne Formation was deposited in a marine environment with restricted bottom circulation and often with anaerobic conditions. In places the formation may contain sandstones which are generally considered to be of turbiditic origin (De' Ath and Schuyleman, 1981; Harms et al, 1981).

Remarks

The Norwegian Lithostratigraphic Nomenclature Commitee formally proposes abandonment of the name "Kimmeridge Clay Formation" for Upper Jurassic claystones encountered north of the Mid-North Sea High. The committee further recommends substitution of the names "Mandal Formation" (in the Central Graben area) and "Draupne Formation" (in the Northern North Sea) for intervals formerly termed Kimmeridge Clay Formation in those areas. The principal reasons for this revision are: (i) distance from type area, and (ii) change in meaning of the term "Kimmeridge Clay Formation" from area to area.

The type area for the Kimmeridge Clay Formation is Kimmeridge Bay in Dorset, southern England (e.g. Arkell 1947). There the unit consists of dark, organic-rich claystones of Kimme-ridgian to Volgian age (using Boreal stage terminology). The term was extended by Rhys (1974 and 1975) into the Southern North Sea to describe a unit of comparable age overlying Oxfordian limestones (Corallian Formation) in type well 47/15-1. Deegan and Scull (1977) further extended the Kimmeridge Clay into the Northern North Sea to denote a generally highly radioactive, generally low velocity claystone sequence. The age range of the formation was broadened to include part of the Oxfordian and Ryazanian. It was remarked that the sediments in the Southern North Sea were less radioactive (less than 60 A.P.I, units compared with 100-200 A.P.I, units in the north). However, the low seismic velocities shown by both units were considered sufficient grounds to justify a correlation.

Deegan and Scull did not specifically discuss the application of the term "Kimmeridge Clay" to the Central Graben region of the Central North Sea. Nevertheless, the name is in common usage there (e.g. Ofstad, 1983). It has, among other meanings, been taken to denote: (i) all claystones of Upper Jurassic age regardless of log character, or more usually, (ii) only the upper, most highly radioactive claystone unit of Volgian-Ryazanian age. To the northwest, in the Norwegian-Danish Basin, a similar deposit is present (the Tau Formation, described in this publication). This unit has never been referred to the Kimmeridge Clay Formation but is nevertheless a typical Upper Jurassic organic shale. It is of Kimmeridgian-Volgian age and occupies a lower relative position in the overall Upper Jurassic shale sequence than the Central Graben "hot shales". (Table 4). A connection between the two deposits across the Southern Vestland Arch is most unlikely.

In extending the Kimmeridge Clay Formation from the type area to the Northern North Sea (a distance of approximately 1300 km) the stratigraphic meaning of the name has varied considerably (Table 5). It is recognised that deposits of this type were laid down over a very wide area in intervals of the late Jurassic, the widespread deoxygenated bottom conditions reflecting the combined effect of paleogeography with general sea level rise (e.g. Tyson et al., 1979; Ziegler 1982). However, acceptance of this overall regime should not alone be taken as a basis for lithostratigraphic classification. The nature and timing of the organic shales appears to have varied according to the evolution of individual basins. Use of the generic term Kimmeridge Clay Formation is a potential cause of mistaken correlation and does not further the understanding of inter-basin relationships. Replacement of the name is a more palatable alternative to its continued extension northwards to the Arctic and Russia, where alternative nomenclature already exists. It therefore seems appropriate to limit the "Kimmeridge Clay Formation" of the North Sea to to the area south of the Mid-North Sea High, as described by Rhys (1974). The Norwegian Lithostratigraphic Nomenclature Committee proposes substitution of the name "Draupne Formation" for the "Kimmeridge Clay Formation" of the Northern North Sea as defined by Deegan and Schull (1977). It is suggested that the name "Mandal Formation" should be applied specifically to the "hot" shales of Volgian-Ryazanian age in the Central Graben region (Table 4), following the precedent set by Hamar et al. (1982).

home	previous page