Thrusted Coal Measures at Ffos Las Opencast Coal Site, Carmarthenshire

Image: © S Dumpleton Taken: 1 Mar 1994

This is Ffos Las opencast site near Trimsaran in the Gwendraeth Valley, Carmarthenshire (Dyfed, as it was then) at the height of its production in 1994. The site was huge and very deep (nearly 200m at its maximum, I think), and was of considerable geological note for its exposure of a major Hercynian thrust system (the Llannon-Trimsaran Disturbance) which caused multiple thrusts, folds, repeated sequences and incompetent deformation structures in the relatively weak Coal Measures shale/coal/seatearth sequences. The same structural disturbances previously caused severe mining problems at deep mines nearby - notably Cynheidre, where I worked as a geologist. The centre part of the photo shows folded and thrusted roof sandstones (mid-grey) overlying the Big Vein coal seam (appears very dark grey-black) and associated shales (dark grey). After the opencast mine finished production in 1997, it was restored and developed in to the Ffos Las racecourse. It's hard to believe that the huge excavation in the photo is now in the middle of the racecourse oval! Taken with a Zenit 'E' camera on Kodachrome 64 transparency film.

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