SUMMARY
Study of cyclic sedimentation in the Coal Measures is impeded by confused terminology and ideas. It is suggested that the first steps in the investigation of an area or sequence where cyclic sedimentation is suspected should be:
(1) to determine statistically if a modal cycle is present and to define that cycle,
(2) to erect a composite sequence representative of the succession.
The Coal Measures of the East Pennine (Yorkshire‐Derbyshire‐Nottinghamshire) Coalfield. England, are examined to illustrate the application of this idea. The succession shows a modal cycle of non‐marine shale followed upwards by seat‐earth with secondary modes (also non‐marine sediments) made up of shale—siltstone—shale—seat‐earth and shale—siltstone and sandstone—shale—seat‐earth. The composite sequence for the whole succession is marine shale—non‐marine shale—siltstone and sandstone—non‐marine shale—seat‐earth.
Consideration of cycle types, horizontal and vertical variation and thickness, lead to the suggestion that sedimentational controls played the major part in the development of the cyclic succession in the Coal Measures of the East Pennine Coalfield. Only three horizons are exceptional and suggest the possibility of regional diastrophic controls or world‐wide changes of sea level.
SUMMARY
Tonsteins from Westphalian Coal Measures in England are compared mineralogically and chemically with tonsteins of volcanic origin from coalbearing sequences of Namurian and Westphalian age in Scotland. Differences are apparent between tonsteins occurring as partings within coals (“coal tonsteins”) and those interbedded with inter‐seam sedimentary rocks (“non‐coal tonsteins”). The coal tonsteins show higher titanium values and in some cases contain minerals of the goyazite series. Sedimentological, mineralogical and chemical evidence is reviewed and the conclusion reached that all tonsteins examined could have originated as thin layers of volcanic ash. Subsequent alteration depended upon the environment of deposition into which the ash fell.
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