A Recce at Otley Chevin - Part 1

 

An exposure of Addingham Edge Grit

After visiting Barnsley in the last week of May, to see the Burton Bank quarry and investigate the building stones in the Barnsley Old Town Conservation Area, I started June 2022 by going on another recce with Paul, the group leader of the Sheffield U3A Geology Group – this time to visit Otley Chevin Forest Park, on the south side of Wharfedale in West Yorkshire. 

 

The Geology Trail

Using a leaflet produced jointly by the Leeds Geological Association, the West Yorkshire Geology Trust and the Friends of Chevin Forest, our plan was to find the eight locations that are marked with stone sculptures by the local artist Shane Green. 

 

The Geology Trail

Starting off from Sheffield on the M1, we eventually arrived at the East Chevin Quarry car park, having relied on Paul’s Sat Nav to take us on a very convoluted route around the east side of Leeds, when I would have just navigated in an old fashioned way, using his road atlas and following signs to Leeds Bradford Airport. 

 

A section through The Chevin reproduced from the Geology Trail

At the beginning of the path, the first sculpture that we encountered records the Variscan Orogeny, which formed the Pennines in the late Carboniferous and early Permian periods, ending approximately 290 million years ago. 

 

The Variscan Orogeny sculpture

 

The first marker, which shows waves and the moon above it, directed us to an outcrop of thin beds of fine sandstone of uniform thickness, which have been interpreted by Neil Aitkenhead of the British Geological Survey as being tidal laminites, with each bed of sandstone being deposited by the ebb/flow of the sea and differences in thickness attributed to the amount of sediment distributed by spring and neap tides.

 

Geology Trail marker No. 1

 

I counted over 40 individual beds which, according to the leaflet, would imply that over a metre of sandstone exposed here would have been deposited in just over 3 weeks, which would presumably require extremely rapid subsidence of the sedimentary basin. 

 

An exposure of tidal laminites

 

Being unable to access the original paper in the Proceedings of the Yorkshire Geological Society, I would be interested to see how the preservation of such a thickness of soft sediment in a tidal environment and its relationship with the massive cross-bedded Addingham Edge Grit, which occurs at the same level a few metres away, is explained. 

 

A detail of the tidal laminites

 

Continuing up the path, the outcrop of massive Addingham Edge Grit has been quarried extensively, with many exposures visible from the path. It is very conspicuous for having its joint planes very heavily iron stained, which gives the rock a deep rusty red colour in many places.

 

Quarry exposures of the Addingham Edge Grit

I obtained a small sample of sandstone with my Estwing hammer, which is coarse grained, feldspathic and orange/brown in colour, with darker bands that have a very high iron content. On the weathered face, however, it has a developed a patina that lacks the bright iron staining and is quite dull in comparison. 

 

A sample of Addingham Edge Grit

 

After passing the quarry faces, we passed a patch of ground where there was a notable change in the vegetation to bog loving plants, which marks a spring at the junction of the mudstone and the overlying Addingham Edge Grit.

 

Bog loving plants growing at the edge of a spring

Fololowing a path that took us above this formation, we then encountered an unusual feature called the Vacca Wall, which is formed of large upright stones placed at the edge of a steep slope that falls down to the valley below. They were built as field enclosures associated with the vaccary system of cattle farming and several of these can be found in the Pennine area.

 

The Vaccary Wall

 

Somewhere along the walk, we had missed the marker at the quarried crags and the next one that we encountered had a carving of a goniatite, which can sometimes be found in the marine bands in the area. This marks the position of the Great Dib landslip, where large blocks of the Long Ridge Sandstone have slipped down the hillside, during periods when the underlying mudstone was lubricated during periglacial conditions. 

 

Geological Trail marker No. 3

All along the north facing slope of The Chevin, the strata have been prone to landslides and, diverting from the path, we could see an irregular landscape on the slopes below that is dominated by large slipped blocks. 

 

A view of the landscape on the Great Dib Landslide

Making our way along the path, which in places was very muddy after the recent heavy rain, beds of mudstone along its edges have weathered to yellow clay, a feature that I had seen very often when exploring the stream banks in the Coal Measures strata around Sheffield.

 

Beds of mudstone weathered to yellow clay