Subsidence and sedimentation in the Northumberland Trough

SUMMARY The Northumberland Trough has been recognised as a major east-west structural unit across northern England for almost a hundred years. Lying between the Northern Pennine Block to the south and the Southern Uplands of Scotland ridge to the north, the Trough stretches across Britain from the North Sea to the Solway Firth. Two basins have been described within the Trough – the Northumberland Basin in the east and the Solway Basin in the west. The basins are believed to be separated by a shelf, with shallow basement running northwards and continuing the line of the Pennine ridge across north-east Cumbria. The Bewcastle anticline is regarded as a drape over this basement high. The oldest deposits proved in the basins are Chadian (Lower Carboniferous), with no confirmed record of the lowest Courceyan Stage. A complete sequence of more than 3 km of Dinantian and Silesian sediments is known, ranging up to late Westphalian D. Strong differential subsidence in the Northumberland Basin came to an end in the Namurian, and the Westphalian was laid down under conditions of uniform epeirogenic downwarping that effected the marginal blocks in the same way as the Trough. The Solway Basin had very similar Dinantian deposition, but subsidence was more variable in the Silesian and persisted longer, at least until the late Westphalian. Shallow marine and deltaic sedimentation characterise deposition in both basins, with subsidence and rate of deposition having been approximately equal. Marine transgressions and deltaic regressions were a major feature of deposition and caused the development of well-ordered sedimentary cycles of coalbelt type. Four phases of trough filling can be recognised: 1. Progressive marine transgression. 2. Gradual marine regression. 3. Upper delta plain sedimentation. 4. Emergence, with lacustrine sedimentation.