Daryl is right. Lithified coal usually behaves in a very brittle manner
during deformation. What you are probably seeing is cataclastic flowage of
the coal within the fault zone. Cataclastic flow of coal is now known to
produce significant variations in the thickness of coal seams most notably
within thrust belts. In the past, these thickness changes were frequently
attributed to ductile deformation of the coal and many quotes to this effect
can be found in old mining literature. There are not many publications that
I am aware of that relate to cataclastic flow in coal but you will find a
description of it in Marc Bustin's paper...
Bustin, R.M. 1979. Characteristics and mechanisms for the formation of
structurally thickened coal deposits, Southeastern Canadian Cordillera.
Ninth Int. Congr. Carboniferous Stratigraphy and Geology, Abstracts of
Papers, pp. 27-28.
Also, if you want further information on the nature and effects of
tectonically-induced fractures in coal, myself and Rod Gayer have a paper
scheduled for publication in the next volume of the International Journal of
Coal Geology, entitled ...
'The impact of tectonic deformation upon coal seams in the South Wales
coalfield, U.K.'
I believe that publication is imminent.
Hope this is of some use!
Kevin Frodsham
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