Initial Survey and Assessment

 

Geology of the Land of Oak and Iron

J L Durkin MSc. MCIEEM

durkinjl@aol.com
www.durhamnature.co.uk

1. Foreword

Project Summary

This project aims to map, record and interpret the most significant geological sites in the Land of Oak and Iron. This work provides an opportunity to train local volunteers in the skills needed to record geological sites, ensuring that the geology of the area is more widely appreciated and better protected. (Cover shows ironstone with tree trunk fossil)

Project description

A total of 75 potential geological sites had been identified by a desk search of existing information and satellite images.

These sites were surveyed using a standard methodology that collected sufficient information for a site to be considered for designation as a Local Site (also known as Regionally Important Geological Site).

Local Sites or RIGS are locally designated sites of local, regional or national importance for geodiversity and designation often leads to protection under the local planning system. There is no RIGS Group currently active in the region and as a result no geological sites are being designated and protected. To allow for designation a new RIGS group will be convened, either operating at a regional or sub regional level or for the Land of Oak and Iron area only.

Initial discussions had been held with Professor Maurice Tucker of Bristol University (formerly of Durham University) who has specialist knowledge of one of the Land of Oak and Iron’s most significant geological features, tufa – a variety of limestone, formed by the precipitation of carbonate minerals from ambient temperature water bodies. Professor Tucker has provided an initial training weekend open to local volunteers. This encompassed both lectures and field work and provides the basis for establishing a group of trained volunteers to carry out the remainder of the field work. There will be a further 9 training sessions over 3 years led by a local expert aimed at both beginners and those wishing to develop their skills to a more advanced level.

Although there are a variety of interesting geological features in the project area, including drumlin fields and exposed rock strata along stream and river valleys, it is hoped that ‘tufa streams’ – water bodies where tufa limestone is deposited, will provide some nationally significant findings.

A key part of each training session is the field work, which gathers information on a number of sites. This information provides the basis for subsequent discussions on RIGS designation and will also provide the material needed for the production of interpretive material on the geology of the Land of Oak and Iron. On site interpretation is to be produced at one of the more significant sites that has good public access. To ensure geodiversity information is available to the widest possible audience, all survey findings will also be made available on line.

The 50 sites identified are in both public and private ownership, but many of the most significant areas are either in public ownership, on publically accessible land or adjacent to rights of way. This high level of access, coupled with training of local volunteer surveyors to act as advocates for the high quality geodiversity of the Land of Oak and Iron will provide an excellent opportunity to further public understanding and appreciation of natural heritage. Greater public awareness and understanding will in turn ensure that the areas geodiversity is protected into the future, both directly as new RIGS are designated and indirectly as the cultural value of sites is more widely known.

When sites receive RIGS designation they are recognised by the planning system and protected into the future.

2. Survey

The survey was carried out by John Durkin from May to December 2016.

75 potential sites were identified from local knowledge, maps and aerial photos. Each of these sites was visited. The tufa formations cannot be identified in this way, so all streams were walked between the known parameters, which are where summer flow becomes constant and stream size is less than the Pont Burn. This amounted to just over 60 kilometres of stream bank.

A small number of sites, mainly disused quarries and springs on private land, could not be accessed, but could be assessed from a distance or from aerial photos.

Plant stem fossil from Clara Vale

3. Results

A range of high quality sites were recorded, including tufa formations, glacial features, rock exposures and fossil sites.

3.1 Tufa

Seven streams with tufa dams were recorded, in Gateshead and in County Durham. Some of these were found to be more extensive than previously thought. No dams were found in Northumberland, but a calcareous spring with tufa formations was discovered, and this may provide information on the origin of these geomorphological features.

The tufa was of two types, most were dominated by a filamentous alga Vaucheria, with some cyanobacterial films. Less commonly, Vaucheria was absent and the formations differed in structure.

The five tufa dam formations lower down the Derwent Valley and the tufa spring were all Vaucheria type formations, with the two sets of dams higher up the valley the more unusual cyanobacteria type.

All eight of these sites meet the standard for designation as Local Geological Sites, and as a group they are of national significance. Most of these sites are at least partially already in Local Wildlife Sites, and one, at Thornley Wood, is partially in a Site of Special Scientific Interest. The Northumberland spring and parts of most of the others have no designations at present.

Because this group of sites is probably of national significance, all eight sites will be designated separately and initially as Local Geological Sites, even where they are already in Local Wildlife Sites.

Several minor sites with tufa features from dripping water on vertical cliffs were found. In these cases, the strata exposed in the cliffs are also important geological features, and are covered under “Rock Exposures”.

Tufa dams at Thornley Wood

Tufa formations at Dene Burn

3.2 Rock Exposures

Places where the coal measures strata can be seen in cross section occur mainly on the banks of the River Derwent. The best examples are at the Sneep, Shotley Bridge and the Chopwell area. There is also a similar feature on the Pont Burn, where iron salts seep out of the rock face. Many quarries were looked at, but exposures were usually poor, due to infilling or natural succession.

The County Durham bank of the Derwent from Muggleswick to Shotley Bridge is already designated, one of only two existing designations. The Northumberland bank is similar, but not designated. This project will designate the Northumberland bank, probably in two sections, from the Sneep to Allensford and at Shotley Bridge.

Northumberland bank at Shotley Bridge

The second existing designation is on the County Durham banks of the Derwent at Chopwell wood. . This project will designate the Gateshead bank, at Chopwell Crags, which is of considerably higher quality. Chopwell Crags shows good strata exposures, tufa seepages and iron salt seepages.

The Pont Burn has a good section where strata are exposed over several hundred metres and include iron seepages. His will be a new designation.

There are lesser exposures elsewhere. In these cases, they are within Local Wildlife Sites and the most appropriate outcome would be to add “geological interest” notes to the LWS designations.

3.3 Glacial Features

Areas of glacial features such as eskers and drumlins were once extensive in the Land of Oak and Iron area, but have been reduced by sand and gravel quarrying and by urban spread. The best remaining example is at Beda Hills, extending into Chopwell Wood and Hookergate, with a second important area at Reeley Mires. Smaller, less intact features remain at Broad Oak and at Crawcrook and Clara Vale.

The Beda Hills and Reeley Mires areas meet the criteria for designation as Local Geological Sites. The boundaries of these landscape features will be harder to define than those of the more specifically bounded Tufa and Rock Exposure sites.

Glacial formations at Beda Hills

3.4 Fossil Sites

Some of the rock exposures are rich in carboniferous period fossils, mostly of plants. Apart from their scientific value, they are of great interest to the public.

Several key sites were identified, at a disused quarry at Castleside, in the bed of the Tyne at Clara Vale, and in the beds of the River Derwent and the Pont Burn where shingle is deposited. Ironstone in the bed of the Derwent at
Shotley Bridge is particularly rich in fossils (see cover picture).

However, none of these sites was considered to be of Local Geological Site quality in its own right. The boulder bed of the tidal Tyne is a site which is only occasionally accessible, and always somewhat dangerous to access. It is already a Local Wildlife Site, so the LWS document can have a geological note added. The beds of the Derwent and Pont Burn can be similarly documented. The Castleside quarry is privately owned and access is discouraged by the
owners.

4 Summary

Thirteen new Local Geological Sites will be documented and designated. For eleven lesser sites already designated as Local Wildlife Sites, the LWS documentation will be extended to take note of the geological interest. The detailed survey, descriptions and designations will be undertaken in 2017 and 2018.

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