Age: Post-Lower Carboniferous
The Carboniferous marks the time in which there was a sharp drawdown of atmospheric CO2, which produced cycles of glaciation and also led to the deposition of the massive coal measures that were subsequently exploited during the industrial revolution. It is from the study of these these coal measures that the system was erected. The rocks of this period outcrop in the north and north-western part of the county, centred on the Wyre Forest Coalfield. They consist of deposits laid down in a flat, swampy, deltaic environment, ideal for coal formation.
The prevalent Coal Measures lithologies have not been used for aggregate; however igneous intrusions of the same age have been extensively quarried. Igneous intrusions are discordant bodies, a few centimetres to over 100 metres thick, and can be of any length. They are produced when magma is injected along fractures in surrounding rock. The tectonic settings responsible for the emplacement of Carboniferous intrusions have not been established, although it may be related to crustal extension following the Variscan orogeny.
This intrusion occurs in a SSW-NNE trend just north of Kidderminster. It outcrops from Eymore Wood in the south to Coldridge Wood in the north, around 3.5km in extent. The rock consists of basalt and appears to lie parallel with the country rock (Lower Coal Measures Group) and therefore maybe more accurately termed a sill intrusion. It creates small, disjointed ridges along its outcrop (due to faulting) of which some have been exploited for aggregate use. Evidence of this can be verified by the presence of quarries exposing the rock at Witnell’s End. The intrusion must post-date the Lower Carboniferous.
Witnell’s End Quarries, Worcestershire