| Computer Code: |
OALEV |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Ipswichian Stage (QI)
— Holocene Epoch (QH) |
| Lithological Description: |
The formation excompasses the marine, estuarine and terrestrial deposits that were formed in the Oldbury and Avonmouth Levels area during the Holocene transgression. The deposits are dark blue-grey silty clays and silts with subordinate sands and beds of peat, submerged forests and gravel. The deposits rest on a rockhead platform intricately dissected by river valleys, and their upper surface is approximately level at c 4.5 to 7m OD. The river valleys are infilled with gravels and sands that become shelly upwards. Typically two beds of peat are included, up to 0.6m thick; the lower of these forms the lowest unit in the formation except where it rests upon the valley-fill sands and gravels, and was formed c.8500-8000 years BP when a birch forest was inundated by the rising sea. The other formed c 5000-4500 years BP during a slowing down of the rising sea level, and is now found resting horizontally at OD. |
| Definition of Lower Boundary: |
Rests unconformably on Triassic Bedrock. |
| Definition of Upper Boundary: |
Surface. |
| Thickness: |
c.10 to 13m, increasing to c.21m in buried channels. |
| Geographical Limits: |
The Oldbury and Avonmouth Levels, from Berkeley, Gloucestershire, to Portishead, Somerset. |
| Parent Unit: |
British Coastal Deposits Group (COAS)
|
| Previous Name(s): |
Estuarine Alluvium [Obsolete Name And Code: Use TFD]
(ESAL)
|
| Alternative Name(s): |
none recorded or not applicable
|
| Stratotypes: |
| Type Area |
The Oldbury and Avonmouth Levels, from Berkeley to Portihead, on the south shore of the Severn Estuary. Welch and Trotter, 1960. |
| Reference(s): |
| Welch, F B A and Trotter, F M. 1961. Geology of the country around Monmouth and Chepstow. Explanation of one-inch geological sheets 233 and 250. Memoir of the Geological Survey of Great Britain. |
| Allen, J R L. 2000. Sea level, salt marsh and fen: shaping the Severn Estuary Levels in the later Quaternary (Ipswichian-Holocene). Archaeology in the Severn Estuary, Vol. 11, 13-34. |
| Allen, J R L, and Rae, J E. 1987. Late Flandrian shoreline oscillations in the Severn Estuary: a geomorphological and stratigraphical reconnaissance. Philosophical Transactions of the Royal Society of London, B315, 185-230. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
E250
E251
E264
|
