A revised description of the lithostratigraphy of the Kimmerdigian-Tithonian and Kimmeridgian-Volgian boundary beds at Kimmeridge, Dorset, UK

Gallois, R.W.. 2011 A revised description of the lithostratigraphy of the Kimmerdigian-Tithonian and Kimmeridgian-Volgian boundary beds at Kimmeridge, Dorset, UK. Geoscience in South-West England : Proceedings of the Ussher Society, 12 (3). 288-294.

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Abstract/Summary

The type sections of the Kimmeridge Clay Formation and the upper part of the Kimmeridgian Stage are cliff and foreshore exposures close to the village of Kimmeridge, Dorset. The succession is made up of rhythmic alternations of mudstone, organicrich mudstone and calcareous mudstone that contains only minor sedimentary breaks. The exposures provide the only complete section in the UK of the succession adjacent to the Kimmeridgian-Tithonian and Kimmeridgian-Volgian boundaries, and are one of the most complete in Europe at this stratigraphical level. Accurate thickness measurements can be made in the cliffs, but palaeontological collecting is difficult due to their weathered state. In contrast, there are extensive outcrops in a relatively unweathered condition in the intertidal zone. This is where almost all the better preserved fossils recorded to date have been collected from. The cliff and foreshore outcrops are mostly separated by beach deposits that make precise correlation between them difficult. The stratigraphical accuracy with which specimens from the intertidal outcrops have been recorded with respect to the succession exposed in the cliffs has mostly been not better than ± 2 m. The use of ortho-rectified air photographs of the intertidal-shallow subtidal areas combined with digitally rectified photographs of the cliff sections has made it possible to produce more accurate correlations between the cliff and foreshore exposures. These have been combined with a revised description of the cliff sections based on rhythms to divide the succession into numbered units that can be recognised in all the outcrops. The revised classification makes it possible to place samples and/or specimens collected from the cliff and intertidal exposures in the stratigraphical succession with an accuracy of ± 0.1 m or better.