| Computer Code: |
KBSG |
Preferred Map Code: |
notEntered |
| Status Code: |
Full |
| Age range: |
Devensian Stage (QD)
— Devensian Stage (QD) |
| Lithological Description: |
Sand and gravel, with cobbles and pebbles predominantly of Permo-Triassic sandstone and Lower Palaeozoic sedimentary and volcanic rocks in a matrix of medium- to coarse-grained sand; typically pale yellow to reddish brown. Greywacke and granitic clasts are common in subordinate amounts. Esker deposits are typically poorly sorted, cobbly and bouldery, well-bedded with high-angle cross-bedding. Some interbeds of coarse sand. Fluted kame and kettle deposits are typically moderately sorted, thickly bedded, cobbly, commonly in upward-fining steeply tabular cross-bedded or trough cross-bedded units. Glaciofluvial Sheet deposits are typically thickly bedded well-sorted gravels, with interbeds of coarse- to medium-grained sand. Commonly horizontally bedded, but tabular high-angle cross-bedded units common. The upper surface is commonly involuted and beds of laminated and rippled sandy silt and clay with dropstone cobbles are present locally, indicating the presence of temporary glacial lakes. |
| Definition of Lower Boundary: |
Unconformable on older glacigenic sediments, such as till of the Gretna Till or Langholm Till formations, or sandy and silty glaciolacustrine deposits of the Cullivait Silt Formation; locally rests directly on bedrock. |
| Definition of Upper Boundary: |
Locally overlain by Holocene alluvial and raised marine deposits, and peat. Some exposures in sheet deposits are capped by gravelly friable pale brown to reddish brown diamicton (supraglacial flow till) typically 0.3-0.6m in thickness). Involutions and possible frost-wedge casts are present in the upper parts of terraced and kame-terrace deposits. |
| Thickness: |
Variable, typically 3-10m, esker deposits may be > 15m thick, the worked spreads of ice-contact deposits may exceed 10m in thickness locally; kame terrace deposits and sandar are typically 2-8m thick. |
| Geographical Limits: |
Northern margin of the Solway Firth, principally between Dumfries and Gretna, but extending inland to beyond Dalswinton, Lochmaben, Lockerbie and Canonbie. |
| Parent Unit: |
Irish Sea Coast Glacigenic Subgroup (ISCG)
|
| Previous Name(s): |
none recorded or not applicable
|
| Alternative Name(s): |
Nithsdale Kames
|
| Stratotypes: |
| Partial Type Section |
Kilblane Quarry. Exposure in large mound shows 5m of rounded to well-rounded cobble gravel with clasts of greywacke and red-brown Permian Locharbriggs Sandstone. The gravel directly overlies up to 2.5m of horizontally interbedded, light-brown [5YR 5/6] fine-grained sand and silt (poorly exposed to base of working). The gravel occurs as horizontally stratified units, typically 0.5-0.8m thick.
An immediately adjacent exposure shows 0.7m of horizontally bedded cobble gravel, overlying c 1.3m of cross-bedded, poorly sorted cobble gravel with thin (c 5cm thick) discontinous lenticular interbeds of sand. This lower sequence shows moderatly developed large-scale tabular cross-bedding (palaeocurrent towards the southsoutheast). This is a large working with only scattered exposures. Field data card CA 1321. Base of deposit not seen, but angular blocks of fresh sandstone in the quarry floor suggest that the sand and gravel rests directly on sandstone bedrock. A variety of the sedimentary features formerly visible within the Kilblane Sand and Gravel in Kilblane Pit are described and illustrated by Huddart (1999, page 5 and Fig 6).
The section described above is regarded as typical of the moundy (fluted kame and kettle) ice-contact facies. |
| Reference Section |
Brownfield (60m-long excavation in barn). Clayey diamicton (flow till), moderate reddish brown, 0.7m thick. Rests with subhorizontal erosive contact on coarse gravel with cobbles and pebbles of greywacke and orange Permian sandstone. Up to 1.9m thickness of gravel seen (unbottomed). Gravel varies from matrix-rich to open framework, with moderately developed planar horizontal bedding; some upward-fining chanelled units with gravel lags. |
| Reference Section |
Locharbriggs Sand and Gravel Pit, 20m long face. Flat-topped spread of poorly-sorted cobble and boulder gravel (>3.5m thick; base not seen). Poorly developed subhorizontal stratification disrupted by conjugate high-angle normal faulting. Gravel clasts are well rounded to subangular, mainly comprise fine-grained greywacke; some Devonian volcanic rocks, Permian sandstone and ironstone. An interbed of horizontally laminated, pale yellowish brown pebbly silty coarse- to medium-grained lithic sand (0.3m thick) occurs from 2.5 to 2.8m depth. This section is recorded on Field data card CA 1316. An adjacent section (CA 1317) showed a 7m wide by 0.3m thick channel infill, of pale to moderate brown laminated silt and clay, within the gravel. |
| Reference(s): |
| Huddart, D. 1999. Supraglacial trough fills, southern Scotland: origins and implications for deglacial processes. http://ggg.qub.ac.uk/ggg/papers/full/1999/rp041999/rp04.html |
| 1:50K maps on which the lithostratigraphical unit is found, and map code used: |
|
S010
S010
S011
S009
|
