M. Campbell and D. Campbell reported in 2018 that according to the policy announced by the senior author (Campbell, 2017), this paper is based on data derived from the field work produced by the senior author during the mid-1970s as part of his research at Rice University for a Master's degree. This paper covers field and follow-on sampling and evaluations developed from monitoring the literature on siderite genesis to date, including additional laboratory work on new samples obtained at the field sites, including new data on the contained carbonates and preliminary work on siderite remanent magnetism.
Occurrences in the two study areas of so-called ‘clayband’ and “black-band” siderite and zones of siderite-replaced marine fossils and associated sediments are reported in selected sandstone and shale sequences of the upper Atoka Formation of Arkansas and Oklahoma. Outcrops near Pocola, Oklahoma and Hackett, Arkansas were examined to characterize the paleoenvironmental conditions of deposition that may have promoted the genesis of siderite.
Eight types of bedded or redistributed siderite were defined, each showing specific responses to bioturbation, to physical erosion and transport, and to chemical replacement and redistribution. The clay minerals contained within the siderite zones and associated shale consist of kaolinite and illite in nearly equal proportions, with the former also possibly consisting of a kaolinite-type chamosite and the latter consisting of a significant 2M muscovite polytype.
Interpretations based on sedimentary structures, texture and mineralogy of the sediments associated with the siderite zones indicate that specific sequences were likely deposited in a tidal flat or intradeltaic environment in proximity to normal marine conditions. A primary or syngenetic origin is proposed for some of the bedded types of siderite occurrence. Other sequences indicate that marine conditions also prevailed. Physio-chemical requirements for siderite genesis suggest that siderite does not form syngenetically in a marine depositional environment but could syndiagenetically result under normal post-burial conditions involving organic-rich material (organic matter?) or a subsurface environment with a high Fe+2:Ca+2 ratio and low SO3 in solution. These conditions likely promoted characteristic siderization of calcareous material within marine sediments in proximity to or down the paleogeohydraulic gradient from areas of either syngenetically-produced siderite or iron-rich groundwater derived from coal-forming swamps.
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