Computer Code: |
GRZH |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Guadalupian Epoch (PUG)
— Lopingian Epoch (PUL) |
Lithological Description: |
The Grenzanhydrit Formation consists of white, pale grey and pale orange or red-brown anhydrite that is variously described as soft and amorphous or hard and microcrystalline, sometimes friable, brittle or sucrosic. Locally the Grenzanhydrit Formation contains a unit of red-brown and grey anhydritic claystone and mudstone (e.g. 47/13-2) or white, yellow or red, clear to opaque halite (e.g. 47/15-1). |
Definition of Lower Boundary: |
The lower boundary of the Grenzanhydrit Formation is normally marked by a sharp downward change from white and pale grey anhydrite to halite, K/Mg salts and local, redbrown, saliferous mudstones of the Aller Halite Formation. It coincides with a downward decrease in density and velocity and an increase in gamma values. |
Definition of Upper Boundary: |
The top of the Grenzanhydrit Formation is normally marked by a sharp downward change from red-brown anhydritic mudstone and siltstone of the Bunter Shale Formation to white and pale grey anhydrite. It coincides with a sharp downward increase in velocity and density and a sharp decrease in gamma values. |
Thickness: |
Its thickest development is around the northern margin where it reaches 5-8 m (e.g. 36/26-1). Sections of 2-5 m thickness occur over much of the western and southern parts of the basin (e.g. 47/13-2), thinning to 1 m or less close to the southern feather-edge (e.g. 49/26/4). Over the central part of the basin, the formation is usually less than 2 m thick, but is locally absent or below wireline-log resolution. |
Geographical Limits: |
The Grenzanhydrit Formation is widely distributed across 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: 975.5-982.5 m (3200-3224 ft) (Johnson et al., 1994). |
Reference Section |
North Sea well 47/13- 2: 2208-2212 m (7244-7257 ft) (Johnson et al., 1994). |
Reference Section |
North Sea well 49/26- 4 (Rhys, 1974, table 2, fig. 3): 1526.5-1527.5 m (5009-5012 ft) (metric conversion revised) (Johnson et al., 1994). |
Reference(s): |
Cameron, T D J. 1993. 4. Triassic, Permian and pre-Permian 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. |
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. 1980. The evolution of the English Zechstein basin. In: Fuchtbauer, H, and Peryt, T M (eds.) The Zechstein basin with emphasis on carbonate sequences. Contributions to Sedimentology 9, 7-34. |
Smith, D B. 1989. The late Permian palaeogeography of north-east England. Proceedings of the Yorkshire Geological Society, Vol.47, 285-312. |
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. |
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. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
none recorded or not applicable |