Kidderminster Formation

Kidderminster Formation

Age: 245- 228 million years (Triassic, Middle)

Overview

The Triassic Period marks a relatively quiet time in the Earth’s geological history, with remarkably consistent climatic conditions throughout, continuing the trend in the Permian of a hot, dry semi-arid environment. However, underlying this apparent calmness lies the fact that a massive extinction took place at the end of the Permian, marking the end of the Palaeozoic (early-life) and the beginning of the Mesozoic (middle-life) era. The extinction event, though less well known than the end-Cretaceous dinosaur extinction, was far more devastating and resulted in the disappearance of over 75% of the world’s known organisms, which were to be replaced in part, by the ancestors to the dinosaurs. Triassic rocks dominate the central-western and northern part of Worcestershire and were deposited in the space created by the continued subsidence of the fault bounded Worcester Basin. The outcrop extends from Eldersfield in the south, along the Severn Valley to Kidderminster in the north. The outcrop is also wider in the north than the south, extending east to Bromsgrove and Redditch. In the south, the strata form the low ground from the western Hills to the Rhaetian scarp slope on the east side of the Severn. The rocks themselves were deposited in a broad, arid, coastal plain.

Lithology

Formerly known as the Bunter Pebble Beds and named after the exposures in and around Kidderminster, the unit has a linear outcrop pattern, extending NNE from the Stour-Severn confluence through to Kinver Edge. There is a small faulted linear slice of the rock just north of Blakedown, and a larger outcrop running along the SW edge of the Lickey-Clent Hills range, extending up to Hagley. A thin outcrop runs along the northern edge of the range from Barnt Green to Rednal. The unit consists of cross-bedded red-brown sandstones and pebble conglomerates in a sandy matrix. The clasts are dominantly brown/purple quartzites, with occasional sandstones, limestones and other minor clasts. The conglomerates appear to thin out towards the top of the sequence. Around the slopes of the Lickey Hills, a quartzite breccia is seen, composed of clasts from the Lickey Quartzite. This is believed to be scree from the Lickey Hills, which may have been upstanding at this time. The breccia would have formed before the rest of the formation was deposited. The rock itself was laid down during flash-flood events on a broad, flat arid desert plain. Exposures of the unit are common, especially in and around Kidderminster, where numerous road cuttings and natural exposures occur, alongside man-made cuttings and caves. The formation was also formerly well exposed in quarries around the Clent Hills, but these have now been infilled.

Sites

Hagley Hall Quarry, Worcestershire

Sling Gravel Pit, Worcestershire