Computer Code: |
HL |
Preferred Map Code: |
notEntered |
Status Code: |
Full |
Age range: |
Asbian Substage (CR)
— Brigantian Substage (CX) |
Lithological Description: |
[Obsolete: use OHL] Hard dark grey crinoidal oolitic bioclastic limestone with interbedded dark grey shales and mudstones. |
Definition of Lower Boundary: |
Boundary is marked by the incoming of more massive oolitic and crinoidal rocks above the relatively unfossiliferous calcite-mudstones of the Clifton Down Group or, where present, the Middle Cromhall Sandstone. |
Definition of Upper Boundary: |
Change to predominantly arenaceous sandstone facies of the Upper Cromhall Sandstone or at the Sub-Namurian unconformity. |
Thickness: |
54m |
Geographical Limits: |
Bristol and north Somerset area. Lateral facies change to west South Wales and Forest of Dean. |
Parent Unit: |
none recorded or not applicable
|
Previous Name(s): |
Vaughans D1 Zone [Obsolete Name and Code: Use HL]
(-4708)
|
Alternative Name(s): |
none recorded or not applicable
|
Stratotypes: |
Type Section |
Avon Gorge, Bristol, between the Suspension Bridge and Hotwells. |
Reference(s): |
Kellaway, G A and Welch, F B A. 1955. The Upper Old Red Sandstone and Lower Carboniferous rocks of the Bristol and the Mendips compared with those of Chepstow and the Forest of Dean. Bulletin of the Geological Survey of Great Britain, No.9, p.1-21. |
Green, G W and Welch F B A, 1965. The geology of the country around Wells and Chedder. Memoir of the Geological Survey of England and Wales, Sheet 280. |
Kellaway, G A and Welch, F B A. 1993. Geology of the Bristol district. Memoir of the British Geological Survey Special Sheet [England and Wales]. |
1:50K maps on which the lithostratigraphical unit is found, and map code used: |
E264
E265
E279
E280
E281
E250
E251
|