The BGS Lexicon of Named Rock Units — Result Details

Lista Formation

Computer Code: LIST Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Paleocene Epoch (GP) — Paleocene Epoch (GP)
Lithological Description: The mudstone facies of the Lista Formation is characterized by non-calcareous, blocky, bioturbated, non-carbonaceous and non-pyritic mudstone. In deeper parts of the basin the mudstone is extremely fine grained, grading to true claystone, often with irregular, listric fracture surfaces. The dominant colour is pale green-grey to grey-green, with subordinate pale yellowish grey, red-grey, red-brown and dark grey. Much of the mudstone is unbedded, especially in the upper part, but moderately fissile and commonly darker mudstone or claystone occurs in the basal part of the unit. The degree of fissility is directly related to the intensity of bioturbation, with the mudstones in the middle and upper parts of the formation commonly being totally homogenized. Zoophycos burrows, preserved as thin inclined layers with distinctive chevron markings in cross-section, are commonly observed in cores. The mudstone is generally non-calcareous, but is locally highly calcareous in the south Central Graben. Siderite is commonly present as concretions. Calcareous mudstone is encountered in southern parts of the Central Graben, apparently reflecting the incorporation of disseminated chalk reworked from the Cretaceous or early Paleocene. The associated sandstones are variable in character. They mostly range from fine to medium grade and display varying degrees of cementation. Conglomeratic sandstones are present at some levels, especially in the Central Graben, with the coarse fraction being composed exclusively of fragments of chalk or penecontemporaneous mudstone. Sandstone lithologies are discussed in more detail below (refer to Heimdal Sandstone Member, Mey Sandstone Member). Thin, argillized, primary air-fall tuff layers are present in the lower part of the formation. Sand-grade, green to brown reworked ash is a prominent feature of the Mey Sandstone Member in parts of the Outer Moray Firth area, where it occurs as discrete volcaniclastic units (Balmoral Tuffite, e.g. 14/25-1) or disseminated in tuffaceous sandstones (refer to Mey Sandstone Member).
Definition of Lower Boundary: In mudstone facies, the lower boundary of the Lista Formation is marked by a downhole change from varicoloured, commonly waxy mudstone or claystone to grey, silty, carbonaceous mudstone of the Maureen Formation (unit 2). This boundary commonly corresponds to the base of a small gamma-ray peak, below which gamma-ray values decrease progressively (e.g. 16/18-1, 14/25-1, 29/8b-1) or sharply (e.g. 3/8a-5A). The boundary is also associated with a zone of relatively low mudstone velocity; this helps to identify the boundary where more than one gamma-ray peak is present. In parts of the southern and western Central Graben, mudstone of the Lista Formation appears to rest directly on a unit of reworked chalk (e.g. 21/8-1), in which case the characteristic gamma-ray peak is not displayed.
Definition of Upper Boundary: In mudstone facies, the top of the Lista Formation is recognized by a downhole change from dark grey, carbonaceous and commonly laminated mudstone of the Moray Group to paler, often greenish, poorly laminated mudstone. This change is accompanied by a marked increase in abundance of agglutinating foraminifera, recognizable in cuttings as minute sandy aggregates, often in tubular form (Bathysiphon). On wireline logs the boundary between Moray Group and Lista Formation mudstones is marked by a downhole decrease in gamma values (e.g. 16/18-1, 29/8b-1). Where sandstone is present at the base of the Moray Group (e.g. 14/25-1) there is no characteristic log signature to identify this boundary. The top of the Lista Formation is in mudstone facies over most of the region, but locally sandstone is present at or very near the top (e.g. 15/24-1; 22/2-2). In such cases, it may be difficult to determine whether the sandstone belongs to the Lista Formation or to the overlying Moray Group unless core samples or biostratigraphic data are available.
Thickness: The Lista Formation reaches over 600 m in the Outer Moray Firth area (e.g. 15/18-2), where the Mey Sandstone Member is thickest.
Geographical Limits: The Lista Formation occurs throughout the basinal area of the Central and Northern North Sea, with its western margin being erosional. Lott & Knox (1994) extended the geographical range of the Lista Formation to include the Southern North Sea.
Parent Unit: Montrose Group (MONT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Norwegian Sector North Sea well N25/11-1 (Deegan & Scull 1977, p.33, fig.41): 2872.5-2917.5 m (9425-9573 ft) below KB. 
Reference Section  North Sea well 3/8a-5A: 1718.5-2042 m (5638-6700 ft). 
Reference Section  North Sea well 16/18-1: 2460.5-2750.5 m (8073-9024 ft). 
Reference Section  North Sea well 14/25-1: 1583-2160.5 m (5193-7088 ft). 
Reference Section  North Sea well 29/8b-l: 2712.5-2767.5 m (8900-9080 ft). 
Reference(s):
Mudge, D C and Copestake, P. 1992. Lower Palaeogene stratigraphy of the northern North Sea.Marine and Petroleum Geology,9,287-301. 
Isaksen, D and Tonstad, K. 1989. A revised Cretaceous and Tertiary lithostratigraphic nomenclature for the Norwegian North Sea. NPD-Bulletin No.5 
Mudge, D C and Copestake, P. 1992a. Revised Lower Palaeogene lithostratigraphy of the Outer Moray Firth, North Sea. Marine and Petroleum Geology 9, 53-69. 
Knox, R W O'B and Holloway, S. 1992. 1. Paleogene of the Central and Northern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
Deegan, C E and Scull, B J. 1977. A standard lithostratigraphic nomenclature for the Central and Northern North Sea. Report of the Institute of Geological Sciences, 77/25; NPD Bulletin No.1. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable