Tedd ASSI

The green mudstones at Tedd have yielded a diagnostic miospore suite allowing the Tedd Formation to be dated as Lower Devonian age, some 375 million years old. The rocks exposed at Tedd form part of the Tedd Formation. They have been dated by the occurrence of microscopic plant spores and have been shown to be Lower Devonian in age, some 375 million years old. Given the complicated nature and varying ages of rocks in this general area, the ability to date the rocks at Tedd is of particular importance.

While the Tedd Formation consists mainly of red-beds, comprising various grades of sandstones together with siltstones and mudstones, the outcrop at Tedd offers the only horizon of green mudstones found to date. These rocks formed within an ancient inland basin, their red colour being due to the presence of oxidised iron minerals. Green or grey mudstones developed where standing water, possibly a lake, prevented oxidation of the iron minerals. It is only in this latter situation that plant pollen or spores are likely to be preserved. That the lake was temporary, possibly seasonal, is shown by the presence of well preserved small scale desiccation cracks formed by periodic drying, while preserved ripples show that occasional flowing water was also present.