Physical properties and micromorphology of till deposits from Talla Earth Observatory, Southern Uplands, Scotland

This factual report describes the 2007 field program at BGS’ Talla Earth Observatory, in the Scottish Southern Uplands, UK. The work involved 12 trial pits with logging of pit walls, soil sampling for particle size analysis and undisturbed sampling for thin sections and micromorphological analysis of a till and a hard pan in moranic deposits. The tills of the Langholm Till Formation (of McMillan & Merritt, 2012) are technically ‘coarse soils’ from a BS5930:1999 ground engineering perspective; typically very dense/hard, very wellgraded silty sandy gravels with a matrix dominated by silt and sand. In thin section the till sandmatrix-supported gravel clasts show a preferred alignment orientated suggesting a micro-fabric indicative of a subglacially deposited till. Clast lithology includes sandstone, siltstone and mudstone, and are consistent with the local bedrock lithology. Cobbles and boulders are often ‘very strong’ from a geotechnical perspective, but may have weaker ‘rotten’ crust in valley floor settings. The work provides new data on the geotechnical properties of Scottish tills and enhances our understanding of the physical and hydrological properties of commonly encountered Quaternary deposits that occur in the Talla Burn and nearby upland catchments.