Geology in Canklow Wood - Part 1

 

A detail of ironstone pellets and casts

Having got 2021 off to a good start with a further exploration of the geology of Shirtcliff Wood and Bowden Housteads Wood, on the first day of February – coinciding with week 47 of the COVID-19 Pandemic – I took advantage of a cloudless day to explore Canklow Wood in Rotherham.

 

A distant view of Canklow Wood

This ancient woodland occupies a large part of a distinctive escarpment to the south of Rotherham, which is capped by the Rotherham Red variety of Mexborough Rock that runs with a strike NNW-SSE down to Aston and Todwick.

 

A geological map showing the position of Canklow Wood

The Rotherham Red sandstone was once extensively quarried along its length, with the old workings clearly visible on LIDAR over a distance of more than a kilometre but, apart from the area that was transformed into Boston Park in 1876, rock outcrops aren't that easy to access.

 

A LIDAR map showing old quarries

While undertaking the survey of RIGS (Regionally Important Geological Sites) back in 1996, I briefly visited some of the quarries that were still accessible and again in 2010, when the site was resurveyed after the South Yorkshire RIGS Group was incorporated into the Sheffield Area Geology Trust (SAGT); however, when searching for these more recently from the top path, I found that the trees had grown so much that I completely lost my bearings.

 

Canklow Wood in 1996 and 2010

This time, having investigated the entrances and paths that are marked on various maps, I entered the wood on the West Bawtry Road, near to Canklow roundabout, and continued up a well worn track that is embedded with innumerable irregular blocks of red sandstone.

 

The track up to the old quarries

Even with the trees bare of leaves, it wasn’t easy to navigate around the upper slopes, which is criss-crossed by various paths and much of the ‘hills and holes’ landscape left behind after the quarrying ceased is wooded with dense undergrowth.

 

The approach to the old quarries

Eventually finding one of the two areas in Canklow Wood that are now described as Local Geological Sites, there were enough good outcrops to enable me to find a range of sedimentary structures in the Mexborough Rock that I had not encountered before. 

 

Large scale cross-bedding

The British Geological Survey describes the setting of this rock as fluvial in origin, with the sediments ranging from coarse to fine-grained and, in very many of the outcrops, large scale cross-bedding - reflecting deposition in a large channel - can clearly be seen from a distance.

 

Cross-bedding

 

Looking closer at this massive sandstone, smaller scale finer cross-bedding is also visible and, although I didn’t see any of these in situ, I noted that some of the discarded blocks have concentrations of ironstone pellets on their bedding planes.

 

A detail of the bedding plane on a loose block