Douglas coalfield model information

Valley of the Douglas Water, south-west of Douglas taken from Hazelside road-end. Lanarkshire. Looking north-east.

This 3D model of Upper Carboniferous bedrock in part of the Clyde catchment covers about 70 km2 of terrain surrounding the valley of the Douglas Water from the villages of Douglas to Carmacoup, and extending to Coalburn in the north-west.

The model was built by BGS in 2011 as part of the CUSP project; CUSP has developed a range of models of the bedrock and superficial deposits at various scales within the Clyde catchment and Glasgow conurbation.

This model is based on borehole, mining and 1:10 000 scale mapped evidence, and extends to -1.5 km depth.

Modelled surfaces

Modelled surfaces commonly have an approximately 150 m node spacing. The model is best viewed between scales of 1:25 000 to 1:100 000 with two times vertical exaggeration.

Data distribution and density was extremely variable across the model; some areas of the model are well constrained (e.g. coal seams in the vicinity of Coalburn) whilst others are less well so (e.g. in the centre of the syncline between Douglas and Glespin).

The modelled area contains the Douglas Coalfield, an area of previous deep mining and current, open cast coal, operations from the Upper Carboniferous Limestone Coal Formation, Upper Limestone Formation and Coal Measures Scotland Group.

The model contains the most significant geological faults cutting the rock strata, which are generally oriented north-east–south-west or north-west–south-east. The dominant structure is a north-east–south-west trending syncline and graben defined by the Pentland–Kennox, Carmacoup and Kerse Loch faults.

Four coal seams are included in the model as mining of these seams has provided a wealth of good quality mine abandonment plan information. In addition five other stratigraphic surfaces are included to link regionally to models of the nearby Central and Ayrshire Coalfields.

Tectonic history

The tectonic history of the basin is complex, with oblique dextral strike slip interpreted at a major fault step over on the north-east–south-west structures from Limestone Coal Formation times, major unconformities developed during Passage Formation times, a Coal Measures growth syncline and subsequent late Variscan basin tightening and fault reversal in the uppermost Carboniferous.

As a result it appears that, in the model, the Coal Measures strata are folded into a tight syncline, whilst deeper strata are not so steeply dipping. This is interpreted to be due to a reversal of earlier extensional faults lower in the succession coeval with folding in the upper parts of the succession.

Reference

Monaghan, A A.  2012.  Model metadata report and geological interpretation for the Clyde, Douglas Basin model.  British Geological Survey Internal Report, IR/12/003. 28pp.