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Lista Formation

Rogaland Group

Unit definition

The Lista Formation is attributed to the non marly, bioturbated and poorly laminated greenish grey claystones and mudstones stratigraphically located between the Våle and the Sele Formations (Fig. 65).

Fig. 65. Lithostratigraphic summary chart of the Lista Formation (color) with members.

Name

The Lista Formation was given name by Deegan & Scull (1977).

Derivatio nominis

The formation is named after the Lista district, onshore Norway, and the Lista Spur structure (Lista Fault Block Complex) in the Norwegian-Danish Basin.

Type well

Norwegian well 2/7-1 (Fig. 66). Depth 2918 to 2873 m RKB, coordinates N 56°25'44.68", E 03°12'14.21". No cores. Defined by Hardt et al. (1989).

Fig. 66. Well 2/7-1. Composite log Rogaland Group. Stratigraphic position of the Lista Formation is outlined in the stratigraphic column to the right.

Reference wells

Norwegian well 15/9-11 (Fig. 67). Depth 2386 to 2308 m. Coordinates N 58°24'02.53", E 01°53'41.79". 10 m cores from the lowest part of the formation. Defined by Hardt et al. (1989).

Norwegian well 16/8-1 (Fig. 68). Depth 1749 to 1708 m. Coordinates N 58°27'24.80", E 02°25'56.80". No cores. Defined by Hardt et al. (1989).

Norwegian well 9/11-1 (New, Fig. 69). Depth 1483-1592 m RKB. Coordinates N 57°00'41.40", E 04°31'40.60. No cores.

Fig. 67. Well 15/9-11 composite log Rogaland Group. Stratigraphic position of the Lista Formation is outlined in stratigraphic column to the right.

Fig. 68. 16/8-1 composite log Rogaland Group. Stratigraphic position of the Lista Formation is outlined in stratigraphic column to the right.

Fig. 69. 9/11-1 composite log Rogaland Group. Stratigraphic position of the Lista Formation is outlined in stratigraphic column to the right.

Composition

The Lista Formation consists of pale green-grey to grey-green shales, with subordinate pale yellow-grey, red-grey, red-brown and dark grey zones. The shales are generally non-tuffaceous, non-calcareous, non-carbonaceous, blocky, bioturbated and poorly laminated. The degree of fissility is directly related to the intensity of bioturbation (Knox & Holloway, 1992), with the mudstones in middle and upper parts being totally homogenized. Zoophycos burrows are common. Occasionally, the Lista Formation contains stringers of limestone, dolomite and pyrite. Thin argillized, primary air-fall tuff layers are present in the lower parts of the formation (Knox & Holloway, 1992).

Representative core photo examples of mudstones of the Lista Formation are shown in Fig. 70.

Fig. 70. Core photographies of Lista Formation well 35/10-2. Left: Sediments are composed of bioturbated green claystone with common purple red patches. Right: Nice example of Zoophycos burrows in sediments. Photographies by L. Vergara and H. Brunstad.

The examples show mudstones of dominantly green grey colour, and with purple red patches. As can be seen the mudstones have a mottled and poorly laminated look, which can be explained by heavy bioturbation. Zoophycos (Fig. 70), Chondrites and Planolites are common trace fossils in the Lista Formation.

Wire line log characterization

The shales of the Lista Formation are generally characterized by intermediate wire line log readings, but there is considerable variability, and several internal zones with high gamma-ray readings occur, representing flooding or condensation surfaces. Velocity logs display spikes of high acoustic velocity that can be related to thin beds or nodules of carbonate.

Lower boundary

The lower boundary of the Lista Formation is synonymous with top of the Våle Formation. The boundary is picked at the top of a trend of overall increase in gamma-ray response and general reduction in velocity. Lithologically the boundary is picked at the top of an upward decrease of carbonate content in the mudstones.

Upper boundary

The upper boundary of the Lista Formation is usually well defined when the upper parts of this formation or the lower parts of the overlying Sele Formation are not sandy. Typically, the boundary can be seen as an abrupt upwards increase in the gamma-ray response from the Lista Formation, often with a well defined peak in the lowest part of the Sele Formation. Lithologically, the boundary can be seen as an abrupt transition from green-grey, bioturbated mudstones of the Lista Formation into dark grey to black laminated shales with only occasional bioturbation.

Thickness

The Lista Formation including sandstone members reach thickness of more than 500 m (523 m in Norwegian well 25/4-1). In the Viking Graben shale thickness of the Lista Formation varies between 100 and 200 m. The formation generally thins towards the highs where thicknesses are less than 50 m. When the Lista Formation is thin it usually contains no sandstones.

Isochore map LISTA-VÅLE from well data

Seismic characterization

The base of the Lista Formation is associated with the change from higher density and higher acoustic velocity of the Våle Formation into the lower velocity and lower density Lista Formation, giving a positive acoustic impedance contrast.

The top of the Lista Formation is commonly associated with a well expressed, extensive seismic event, where the higher velocity Lista Formation is underlying a low velocity zone in the lowermost part of the Sele Formation, and thus giving a positive acoustic impedance contrast.

When sandstones are present in the Lista Formation this is often associated with thickening as well as semi-continuous, undulating internal reflectors and lense shapes, mounds and trough infills.

Age

Late Middle to Late Paleocene (Late Selandian to Early Thanetian).

Biostratigraphy

The top of the Lista Formation is assigned to last down-hole occurrence of a dinocyst assemblage dominated by Apectodinium spp. The body of the formation contains in order from young to old: The base of the Lista Formation is slightly below the top ACME Palaeoperidinium pyrophorum and top Isabelidinium ?viborgense. In terms of shelly microfossils the top of the formation contains a low diversity agglutinated foraminiferal assemblage.

The body of the Lista Formation contains the last occurrence (tops) of the following agglutinated taxa in the shown (most likely) stratigraphic order:

The base of the Lista Formation agrees with the youngest occurrence of Cenosphaera lenticularis.

The Lista Formation belongs in the foraminiferal Zone NSR2A - 2B, A. ruthvenmurray - R. pauperum (Gradstein & Bäckström, 1996), and the dinocyst Zones D3b - D4 in Luterbacher et al. (2004). The age is Late Selandian through Thanetian, late Middle through Late Paleocene.

Some diagnostic microfossils of the Lista Formation are shown in Fig. 71.

Fig. 71. Some diagnostic microfossils of the Lista Formation. Palaeoperidinium pyrophorum (Ehrenberg 1838 ex O. Wetzel 1933a) Sarjeant 1967b. Dorsal view of dorsal surface; 450x. Areoligera gippingensis Jolley 1992. Ventral view. Range of type material: overall length = 32-42 µm, overall width = 45-59 µm, process length = 15-33 µm. Alisocysta margarita (Harland 1979a) Harland 1979a. Ventral view. Holotype dimensions: length = 44 µm, width = 40 µm. From the ODP Drilling Program at http://www-odp.tamu.edu.

Correlation and subdivision

The Lista Formation can be subdivided into a lower (L1), a middle (L2) and an upper (L3) part which are separated by condensation surfaces associated with specific bioevents (Knox and Holloway, 1992). These condensations are associated by high gamma shales and seem to have a regional importance, and may be related to relative sea level changes (e.g. Mudge and Bujak, 1996).

The base of the L1 zone is picked at the high gamma shale that occurs between the I. ?viborgense and T. cf. delicata dinocyst zones and close to the top of the Cenosphaera lenticularis microfaunal zone. The boundary between the L1 and L2 is taken at the high gamma shales associated with the P. pyrophorum acme, and the boundary between L2 and L3 is taken at a high gamma zone associated with the A. gippingensis acme. The top of the L3 zone is taken at the high gamma peak near the base of the Sele Formation, which is associated with the top of impoverished agglutinated assemblage.

Internally in the Lista Formation several sandstones members are found (Figs. 12 and 13). The Siri Member and Sotra Member seem to have an eastern provenance (Scandinavia), whereas the Mey Member and the Heimdal Member have a western provenance (Shetland Platform).

Links to member descriptions

Geographic distribution

The Lista Formation for all practical purposes has a distribution related to the presence of the Rogaland Group in the Norwegian North Sea. The Sotra Member is found in the area of Måløy Platform and Sogn Graben, and may stretch into the Stord Basin (Fig. 72).

Occurrences of formation tops in wells

Fig. 72. Distribution of the Lista Formation and its sandstone Members.

Depositional environment

Going from the Våle Formation and into the Lista Formation climate became temperate/cooler and the connection with the warmer Atlantic and Tethys oceans became more limited. This had an impact on the water temperature in the North Sea basin, which became cooler. As a response the amount of calcareous plankton became much less.

The Lista Formation was deposited in a marine environment where the earlier calcareous input from microorganisms, and reworking from exposed chalk of the Shetland Group had come to an end. Accordingly the fines deposited in the basin were dominated by siliciclastic minerals. The trace fossils in the sediments in general became smaller and sediments darker, reflecting a less well oxygenated basin in this period.

In the basinal areas of the Viking Graben, Stord Basin and the Central Graben paleo waterdepth was mostly deep marine, bathyal. To the east paleo waterdepth was shallower, extending into upper continental shelf slope or shelf setting. Changes between faint dark purple red and medium grey to dark green colored bioturbated mudstones probably reflect changes in the balance between water circulation and sedimentation rate. The change between rich and abundant bioturbation in the mudstones reflects change from rather oxygen rich and well circulated bottom waters to dysoxic or sometimes anoxic conditions. The silty fraction increases towards the slope wedges flanking the basin to the east and west (UK).

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