Coal measures (Namurian and Westphalian) Blackband Iron Formations: fossil bog iron ores

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Abstract
Blackband iron formations are essentially thin (approximately 0·75 m thick) siderite‐rich (total iron up to 40%), carbonaceous, laminated mudrocks which commonly occur in grey coal bearing sequences in close proximity to coal seams. They exhibit a conspicuous laminated macrotexture made up of carbonaceous and siderite‐rich laminae together with primary textures such as root‐disturbed laminae, sideritized unflattened spores and preservation of plant cell detail. These all point to formation of siderite soon after deposition, in some cases before significant compaction. Their enclosing sediments clearly show that they were deposited in environments intermediate between delta top alluvial floodplains and coastal plain swamps in which small areas were subjected to periods of lacustrine deposition. The presence of varved mudrocks and oil shales in the beds directly above many of the blackband iron formations and the distinctive fine lamination of the blackbands are evidence of such depositional environments. The blackband iron formations are considered to have been formed in a similar way to Recent bog iron ores and are therefore interpreted as fossil bog iron ores. A model for their mode of formation is presented.