Upper delta plain lacustrine and fluviolacustrine facies from the Westphalian of the Durham coalfield, NE England

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Abstract
Facies analysis suggests that the productive Westphalian (Upper Carboniferous) Coal Measures of the Durham coalfield in NE England were deposited on an upper delta plain. Distributary channels crossed the plain and were separated by shallow lakes.Detailed examination of largely three‐dimensional exposures has revealed the existence of nine laterally and vertically interrelated fluviolacustrine and lacustrine lithofacies. Facies 1 and 2 are interpreted as overbank deposits of distributary channels, Facies 3–5 are regarded as deposits of crevasse splay/minor delta systems, and Facies 6–9 are considered to have formed in areas of diminished clastic sediment supply. Facies 4 and 5 are volumetrically the most important. Facies 3–9 are interpreted as representing progressively less energetic conditions of sedimentation across a lake, from the point of entry of a crevasse splay/minor delta system.The distribution and characteristics of the lithofacies indicate that the upper delta plain lakes were completely or effectively enclosed, up to about 8m deep and had wave fetches of the order of 20 km. These lakes were intermittently infilled by the crevasse‐initiated, minor delta systems and, to a relatively minor extent, by overbank flood sediment from channels. Infilled lake surfaces became platforms for plant colonization and peat accumulation.The three dimensional relationships of the various lithofacies provide a model of Coal Measure lacustrine sedimentation, which may have wider implications in extending the model of interdistributary genesis and infilling proposed by Elliott, particularly with respect to detailed facies relationships and to the balance between overbank and crevasse‐derived sediment.