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Abstract

The Pennine basin evolved during Upper Carboniferous times from a deep-water basin in which fine-grained sediments and turbidites accumulated via prograding delta complexes to a fluviatile-dominated environment with extensive coal swamps. A detailed study of a marine incursion (G. sub-crenatum Marine Band) into the fluviatile environment has shown a decrease in kaolinite upwards through the section from nonmarine to marine and increases in: (1) the sum of illite + mixed-layer illite/smectite (I/S); (b) the illite to I/S clay ratio; and (3) the sum of chlorite + vermiculite. These changes reflect a shift in the balance between locally derived sediment and primary, less altered sediment from the rocks in the hinterland. The same explanation is advanced for similar changes noted through much of the Namurian (Tansley borehole). Very slow rates of sedimentation apparently led to metal enrichment in some of the marine shales. The influence of sorting was detected in turbidite sandstones and in the associated mud-rocks; kaolinite is proportionally more important and illite and mixed-layer clay less so, the coarser the sediment. In the coal-swamp environment the fine-grained sediment available in suspension was found to be locally derived and comparable with underclay mineralogy. This material was noted dispersed through coal seams and concentrated in mudrock partings within coals. Kaolinite beds (tonsteins) have been recorded associated with the coals and a volcanic origin proved. In addition, diagenetic kaolinite was found as void and fracture infills.

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