Journal cover Journal topic
Journal of Micropalaeontology An open-access journal of The Micropalaeontological Society
J. Micropalaeontol., 28, 67-85, 2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 4.0 License.
01 May 2009
The biostratigraphy of the Upper Pliensbachian-Toarcian (Lower Jurassic) sequence at Ilminster, Somerset
I. Boomer1, A. R. Lord2, K. N. Page3, P. R. Bown4, F. M. D. Lowry5, and J. B. Riding6 1School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT, UK
2Forschungsinstitut Senckenberg, Senckenberganlage 25, Frankfurt-am-Main, Germany
3SEOES, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK
4Department of Geological Sciences, University College London, Gower Street, London WC1E 6BT, UK
5School of Earth & Environmental Sciences, University of Greenwich, Chatham Maritime, Kent ME4 4AW, UK
6British Geological Survey, Keyworth, Nottinghamshire NG12 5GG, UK
Keywords: Pliensbachian–Toarcian, Ostracoda, Foraminifera, palynology, nannofossils Abstract. Temporary road sections for the A303 bypass at Ilminster, Somerset, revealed Upper Pliensbachian and Toarcian sediments from an alternating limestone–marl facies, in marked contrast to the limestone-dominated Dorset coast succession. The lithostratigraphy is described, with the standard ammonite zonation providing chronostratigraphical correlation. The uppermost Pliensbachian (Spinatum Chronozone) and much of the Toarcian (Serpentinum, Bifrons, Variabilis, Thouarsense and Pseudoradiosa chronozones) of the classic Dorset coast Lower Jurassic sequence are represented by the Beacon Limestone Formation, formerly the ‘Junction Bed’ (a highly condensed carbonate deposit). The Tenuicostatum Chronozone is largely missing from the sequence. Elsewhere in southern and eastern England this interval is poorly or rarely exposed. The argillaceous units have yielded rich microfaunas and -floras (foraminifera, ostracods, calcareous nannofossils and palynomorphs), the biostratigraphical distributions of which are analysed and discussed in relation to contemporary evolutionary patterns and other UK records. This study provides an insight into the micro-biostratigraphy of the Late Pliensbachian to Toarcian interval for onshore southern England.

Citation: Boomer, I., Lord, A. R., Page, K. N., Bown, P. R., Lowry, F. M. D., and Riding, J. B.: The biostratigraphy of the Upper Pliensbachian-Toarcian (Lower Jurassic) sequence at Ilminster, Somerset, J. Micropalaeontol., 28, 67-85,, 2009.
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