|
Article |
Department of Geology, The University of Exeter, North Park Road, Exeter EX4 4QE UK
Scanning electron microscope (SEM) techniques show that the low-grade metamorphic rocks of Southwest England can yield abundant palynomorphs. The technique is outlined and the character of the material illustrated by new assemblages including Emphanisporites, Dibolisporites and Leiotriletes from the Lower Devonian Meadfoot Group, south Devon.
Progress in the resolution of many problems in the Variscides has been inhibited by lack of site-specific biostratigraphic control. Conventional biostratigraphic techniques have largely failed, particularly for clastic Upper Palaeozoic sequences at low metamorphic grades. However, the application of routine SEM methods has shown that many such rocks may yield palynomorphs. The technique has been applied with considerable success to material from Devonian clastic sequences in Southwest England in a joint programme of research between the University of Exeter and the British Geological Survey, associated with the Cornwall and South Devon Project.
From more than 100 samples routinely collected during the BGS mapping of poorly dated sequences in south Devon (Fig. 1) almost all have yielded some information and many contain well preserved palynomorphs. A local SEM-based biostratigraphy is being formulated for these previously intractable successions. This paper outlines the technique and demonstrates the character of the palynomorph assemblages recovered from a sequence of cleaved interbedded sandstones and mudstones of the Lower Devonian Meadfoot Group, which has generally been considered to be of marine origin.
Method and material. Field samples are prepared following routine palynological procedures (see Playford & Dring 1981) but omitting the oxidation techniques usually employed. The resultant fraction, after centrifuging, is strew
