The BGS Lexicon of Named Rock Units — Result Details

Aller Halite Formation

Computer Code: ALHA Preferred Map Code: notEntered
Status Code: Full
Age range: Guadalupian Epoch (PUG) — Lopingian Epoch (PUL)
Lithological Description: The Aller Halite Formation consists of halite with subordinate interbedded and intergrown K/Mg salts and saliferous mudstones. The halite is generally colourless, locally orange, pink, yellow, white or grey, coarsely crystalline, transparent to translucent, occasionally opaque and moderately hard. The K/Mg salts mainly comprise sylvite and carnallite with rare occurrences of kieserite and are white, pink or red, transparent to opaque, and hard. Mudstones, generally occurring in the upper part of the formation, are redbrown, locally grey-green, soft, amorphous, occasionally hard and locally saliferous and/or anhydritic.
Definition of Lower Boundary: The base of the Aller Halite Formation is normally defined by a sharp downward change from colourless or pink, clear halite to white or grey anhydrite of the Pegmatitanhydrit Formation. The boundary is characterized on wireline logs by a sharp downward increase in velocity and density. The gamma log response to this boundary is variable, although there is commonly no significant downward change. Locally, however, a downhole decrease in gamma values is seen, reflecting the presence of mudstone and/or sylviteenriched halite at the base of the Aller Halite Formation (e.g. 41/25a-l and 49/26-4). Where the Pegmatitanhydrit Formation is locally absent, the Aller Halite Formation rests on the Roter Salzton Formation, coinciding with a sharp downward increase in gamma values, but no significant change in velocity (e.g. 36/26-1).
Definition of Upper Boundary: The top of the Aller Halite Formation is normally marked by a sharp downward change from white or pale grey anhydrite of the Grenzanhydrit Formation to halite, K/Mg salts and local red-brown saliferous mudstones. The boundary is characterized on wireline logs by a downward decrease in velocity and density and a downward increase in gamma-ray values. It is locally less well defined where the overlying Grenzanhydrit Formation is thin (e.g. 49/26-4). Where the Grenzahydrit Formation is locally absent and siltstones of the Bunter Shale Formation rest directly on the Aller Halite Formation, a sharp downward decrease in gamma values and velocity marks the boundary (e.g. 41/25a-1).
Thickness: It thickens into the centre of the basin to approximately 130 m, although its depositional thickness is difficult to determine because many sections have been extensively disrupted by halokinesis.
Geographical Limits: The Aller Halite Formation is present throughout much of the Southern North Sea Basin.
Parent Unit: Zechstein Group (ZG)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  North Sea well 36/26- 1: 982.5-1036.5 m (3224-3400 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 47/13- 2: 2212-2242.5 m (7257-7358 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 49/26- 4 (Rhys, 1974, table 2, fig. 3): 1527.5-1587 m (5012-5206 ft) (Johnson et al., 1994). 
Reference Section  North Sea well 41/25a- 1: 1091-1168.5 m (3580-3834 ft) (Johnson et al., 1994). 
Reference(s):
Johnson, H, Warrington, G and Stoker, S J. 1994. 6. Permian and Triassic of the Southern North Sea. In: Knox, R W O'B and Cordey, W G (eds.) Lithostratigraphic nomenclature of the UK North Sea. British Geological Survey, Nottingham. 
NAM and RGD (Nederlandse Ardolie Maatschappij and Rijks Geologische Dienst) 1980. Stratigraphic nomenclature of the Netherlands. Transactions of the Royal Dutch Geological and Mining Society of Delft. 
Rhys, G H. 1974. A proposed standard lithostratigraphic nomenclature for the southern North Sea and an outline structural nomenclature for the whole of the (UK) North Sea. Report of the Institute of Geological Sciences, 74/8. 
Smith, D B, Harwood, G M, Pattison, J and Pettigrew, T H. 1986. A revised nomenclature for Upper Permian strata in eastern England. 9-17 in Harwood, G M and Smith, D B (editors). The English Zechstein and Related Topics. Geological Society Special Publication No.22. 
Smith, D B. 1989. The late Permian palaeogeography of north-east England. Proceedings of the Yorkshire Geological Society, Vol.47, 285-312. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable