The BGS Lexicon of Named Rock Units — Result Details

Maureen Formation

Computer Code: MAUR Preferred Map Code: notEntered
Status Code: Full, pending ratification
Age range: Paleocene Epoch (GP) — Paleocene Epoch (GP)
Lithological Description: The Maureen Formation is lithologically heterogeneous, including mudstone, siltstone, sandstone, and reworked limestone. The mudstone is light to medium grey and calcareous in the lower part, and characterized in cores by conspicuous, usually dark grey, Zoophycos burrows, preserved as thin inclined layers with distinctive chevron markings in cross-section. Some of the more silty mudstones include abundant chaotically distributed clasts of mudstone and chalky limestone. Some of the limestone clasts are angular; others are well rounded and often display superficial glauconite staining. The sandstone is generally fine to medium grained. Thick units of clean, poorly consolidated sandstone are present locally (e.g. 10/1-1A), but more commonly the sandstone occurs as a series of thinner units (e.g. 16/29-2), often with a chalky matrix. Thin beds of muddy, matrix-supported sandstone with mudstone and limestone fragments are locally present in the upper part of the formation. The reworked chalky limestone is generally fine grained; some units are well bedded and display delicate interlamination of terrigenous mud; others have undergone varying degrees of soft-sediment deformation, leading to oversteepened dips, and small to large-scale contortion. The limestone units usually display sharp contacts with the overlying and underlying mudstone or sandstone. In southern parts of the Central Graben in particular, laterally fed reworked chalk has mixed with axially transported sand to produce mixed lithologies that are difficult to identify precisely on the basis of wireline-log character. The basal limestone in the south of Quadrant 3 locally grades into a calcarenite with abundant skeletal debris.
Definition of Lower Boundary: The base of the Maureen Formation is generally characterized by a rapid downward transition from marl to the limestone of the uppermost Ekofisk Formation. On wireline logs this is taken at the top of the consistent low-gamma Ekofisk limestone; this commonly corresponds to a shoulder on the sonic log, marking the top of a unit of high-velocity Ekofisk limestone (e.g. 22/10a-4, 21/20-1). Where the gamma and sonic markers do not coincide, the boundary is picked on the gamma (e.g. 14/30-1). Where thin limestone spikes occur at the top of the limestone section, these are included within the Maureen Formation. In some sections the basal marl is replaced by sandstone or reworked limestone (e.g. 22/10a-4). In such cases the boundary is usually marked by a downward change from variable to more consistent gamma and sonic traces. Where relatively pure reworked limestone rests directly on Ekofisk limestone (e.g. 22/11-2) a downward change from scattered to consistent dips may be used to define the boundary. In some marginal sections, the Ekofisk Formation is absent, and the Maureen Formation rests directly on Cretaceous chalk or on older formations. In the East Shetland Basin, the base of the Maureen Formation is taken at a downward decrease in gamma values and increase in sonic velocity, corresponding to the contact between Danian marls and limestones attributed to the late Cretaceous. It is possible that the lower, marly unit of the Maureen Formation in this area includes lateral equivalents of the Ekofisk Formation.
Definition of Upper Boundary: Over much of the central North Sea, the top of the Maureen Formation is taken at a downward change from waxy claystone with greenish or reddish tints (Lista Formation) to dark grey, silty mudstone (Maureen Formation). This boundary corresponds to the base of a high-gamma peak. Where the dark grey silty mudstone is missing due to condensation or lateral facies change, the formation top is taken at a downward change to calcareous sandstone, reworked limestone or marl (e.g. 21/8-1). In central and northern parts of the Viking Graben, the unit is difficult to differentiate from the overlying Lista Formation because the upper part of the formation no longer displays the characteristic upward-fining profile on gamma-ray and sonic logs. The top of the formation is taken at the base of a section of consistent and relatively high gamma values (e.g. 3/3-8, 3/4-4).
Thickness: The thickness of the Maureen Formation in basinal areas is highly variable reaching over 400 m in the sand-rich sections of the Outer Moray Firth and the South Viking Graben.
Geographical Limits: The Maureen Formation is well developed in the Central Graben and South Viking Graben (including the Norwegian Sector, Isaksen and Tonstad 1989), where it contains a significant proportion of sandstone; a relatively thin mudstone unit extends over adjacent shelf areas, especially along the western margin of the Central Graben, but also in a thin zone around the Halibut Horst. The western limit of the formation is commonly depositional, unit M1 being overstepped by unit M2, which is in turn overstepped by the Lista Formation. The limit of the Maureen Formation shown on the distribution map corresponds to the limit of the characteristic wireline-log response of upward-increasing gamma values and decreasing velocity. Abundant radiolaria at the base of the Lista Formation further west indicate that a very thin veneer of M2 mudstone extends beyond this limit. Lott and Knox (1994) extended the geographical range of the Maureen Formation to the Southern North Sea area.
Parent Unit: Montrose Group (MONT)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  North Sea well 21/10-1 (Deegan & Scull 1977, p.31, fig.36): 2464-2524 m (8085-8281 ft) below KB. 
Reference Section  North Sea well 16/29-2: 2596-2725 m (8517-8940 ft). 
Reference Section  North Sea well 22/10a-4: 2670-2785 m (8760-9072 ft). 
Reference Section  North Sea well 10/1-1 A: 2386-2793 m (7828-9164 ft). 
Reference Section  North Sea well 21/20-1: 2775.5-2859.5 m (9106-9382 ft). Not recorded in BGS Offshore GeoIndex. 
Reference(s):
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