Cwar yr Ystrad a Cwar Blaen dyffryn
Geology & landscape
Geological Feature: Rock Outcrop · Mining / Industrial: Quarry · Geological Period: Carboniferous · Rock Type: Carboniferous Limestone, Limestone, Shale
Description
Description The two quarries that make up this site, Cwar yr Ystrad a Cwar Blaen Dyffryn, form parts of a large complex of quarries on the northern limestone scarp of the South Wales Coalfield. Cwar yr Ystrad is a linear quarry, cut along the outcrop of the Carboniferous Limestone in a northeast-southwest direction. Cwar Blaen Dyffryn is a crescent-shaped quarry one kilometre further northeast along the escarpment. Both have high sheer vertical faces that show the rock sequence. Access is possible to various parts of this sequence due to the occurrence of benches and quarry roads cut into these faces. Cwar Blaen Dyffryn has not been worked for some time, but Cwar yr Ystrad was worked for limestone until the mid 1990s. The Carboniferous Limestone succession in Cwar yr Ystrad ranges from the top of the Lower Limestone Shale Group through the Oolite Group to the overlying Llanelly Formation. The top of the Oolite Group includes a spectacular palaeokarstic pebble horizon. Palaeosols occur at lower levels but are also well developed in the Llanelly Formation where they contain large calcrete nodules. The section at Cwar Blaen Dyffryn shows the Oolite Group but here demonstrates a unique example of humid climate palaeokarst (Kavorossen Karren). Significant lateral variation occurs within the Carboniferous Limestone between Cwar yr Ystrad a Cwar Blaen Dyffryn which make both sections distinct but complementary. Together these quarries are of great importance to international studies of the Lower Carboniferous palaeoenvironments, palaeogeography and the process of soil formation under ancient tropical climate conditions. Remarks: The site lies within the Brecon Beacons National Park.