Conference Report – Symposium on the Old Red Sandstone, Brecon, October 2014

November 14, 20141:18 pmNovember 12, 2015 4:30 pm
Confluence of the Yukon and Koyukuk Rivers, Alaska, United States, 1941

Braided rivers, flowing across a broad floodplain – a good modern analogue for the Old Red Sandstone environment (Confluence of the Yukon and Koyukuk Rivers, Alaska, 1941, Public Domain)

At the start of October Elliot and Kate presented at the inaugural Symposium on the Old Red Sandstone in Brecon. The Old Red Sandstone is the name given to the rocks formed between about 420 and 360 million years ago when Britain was at the margins of an arid desert. Its predominantly red rocks – the result of the same intense weathering, of iron rich minerals such as mica, which forms laterite soils in hot arid regions today – underlie the bulk of Herefordshire, giving rise to its distinctive fertile red soils.

That fact means that understanding and charting its variation is crucial to us understanding the variation that exists in local building materials across much of our project area. A barrier to this is a high degree of local geological variation that belies the rock’s “Red Sandstone” moniker – or, as the conference organisers put it; it’s not all red and most of it isn’t sandstone. The group includes lithologies from mudstone to cobble conglomerates and varies in colour from olive green to deep red, purple or rusty brown, often within the space of a few centimetres.

Many distinctive units will have been laid down only in the beds of meandering braided rivers and so may be geographically restricted to a few metres of rock. Equally it is becoming clear that both huge floods and long term cessation of sedimentation could be basin-wide phenomena resulting in sandstone/conglomerates and calcretes respectively that can be traced for hundreds of kilometres. Understanding the interplay between these two opposing trends in deposition is as crucial to understanding the distinctiveness of local stones as it is to addressing broader questions regarding the wider environment and mechanics of their formation 400 odd million years ago.

As to what we’ve managed to contribute thus far to advance the issue the answer is, as yet not much. Our talk consisted mostly of a series of open questions tempered with hints and possibilities of answers as yet unforthcoming. For instance how far can distinctive stone from a given town be traced into the surrounding countryside? Is there a reason that green stones seem to be preferred for high status buildings and might this relate to apparent differences in weathering performance? How can the inherent sampling bias that affects stone selected from a quarry be mitigated against? Other interesting ideas came out of discussions with other delegates between talks. One such is that buildings in Bromyard may have utilised stone sourced by digging out the cellars (and if these cases can be reliably identified could this be used as a mapping tool?). Another was the idea of microwaving sandstones till they fall apart to search for microscopic fish fossils that could act as a “fingerprint”. However we are making progress and in working towards submitting a paper to the proceedings we will be clarifying many of these issues.

Written by Elliot Carter

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