| Computer Code: |
BDTI |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Devensian Stage (QD)
— Devensian Stage (QD) |
| Lithological Description: |
Reddish brown, gravelly sandy silty clayey diamicton dominated by locally-derived clasts such as of the Kidderminster Formation (Bunter Pebble Beds) conglomerates, but with a significant proportion of erratics including grey granite from the Southern Uplands, striated volcanic rocks, Eskdale Granite, Ennerdale Granophyre and slates from the Lake District, limestone, flint and marine shells. The tills are typically thinner, more eroded, more weathered and considerably more cryoturbated than those of the Stockport Glacigenic Formation lying to the north of the Wrexham-Ellesmere-Whitchurch-Barr Hill Moraine in Cheshire. |
| Definition of Lower Boundary: |
Sharp, unconformable contact with fluviatile gravel (Four Ashes Sand and Gravel Formation) containing mainly well rounded clasts derived from the Kidderminster Formation (Bunter Pebble Beds) conglomerates and numerous organic-rich lenses of Ipswichian to Middle Devensian age. The diamicton is heavily cryoturbated at the type section at Four Ashes where it has been loaded down into the underlying gravel. |
| Definition of Upper Boundary: |
The ground surface or unconformable contacts with glaciofluvial sand and gravel or younger Quaternary deposits. |
| Thickness: |
3 m at type section. Up to 17 m at Madeley in Telford district |
| Geographical Limits: |
The ground lying within the generally accepted Late Devensian glacial limit in Staffordshire, but outside the Wrexham-Ellesmere-Whitchurch-Barr Hill Moraine in Cheshire. |
| Parent Unit: |
Irish Sea Coast Glacigenic Subgroup (ISCG)
|
| Previous Name(s): |
Unnamed till of Irish Sea provenance at Four Ashes [Obsolete Name and Code: Use BDTI]
(-1340)
|
| Alternative Name(s): |
Stockport Formation
|
| Stratotypes: |
| Type Section |
Disused gravel pit at Four Ashes, Staffordshire, formerly chosen as the type site for the Devensian (Michell et al., 1973). Morgan, 1973 |
| Partial Type Section |
Ketley Grange Opencast Site, Telford Hamblin and Coppack, 1995. |
| Reference(s): |
| Mitchell, G F, Penny, L F, Shotton, F W, and West, R.G. 1973. A correlation of Quaternary Deposits in the British Isles.Geological Society of London Special Report, No. 4.Scottish Academic Press, Edinburgh. |
| Morgan, A V. 1973. The Pleistocene geology of the area north and west of Wolverhampton, Staffordshire, England. Philosophical Transactions of the Royal Society of London, Series B, Vol.265, 233-297. |
| Worsley, P. 2005. The Cheshire-Shropshire Plain. Chapter 5 in Lewis, C A and Richards, A E (editors), The glaciations of Wales and adjacent areas. (Logaston Press.) |
| Hamblin, R J O and Coppack, B C, 1995. Geology of Telford and the Coalbrookdale Coalfield. Memoir of the British Geological Survey, parts of Sheets 152 and 153 (England and Wales). |
| Boulton, G.S, and Worsley, P. 1965. Late Weichselian glaciation in the Cheshire-Shropshire Basin. Nature, 207, 704-706. |
| Worsley, P. 1991. Glacial deposits of the lowlands between the Mersey and Severn rivers. 203-211 in Ehlers, J, Gibbard, P L and Rose, J (editors), Glacial deposits in Great Britain and Ireland. |
| Bowen, D Q. 1999. Wales. Chapter 7 in A revised correlation of Quaternary deposits in the British Isles. Bowen, D Q (editor). Geological Society of London Special Report, No. 23. |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
| none recorded or not applicable |
