Siderite concretions: indicators of early diagenesis in the Gammon shale (Cretaceous).

Journal of Sedimentary Petrology


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The Gammon member of the Pierre shale of the northern Great Plains, USA, contains abundant siderite concretions. The relative depth and time of siderite precipitation can be inferred from the structure, mineralogy and isotopic composition of these concretions. Concretions that formed at shallow depths, early in the history of the sediment, contain a high percentage (75-85%) of carbonate, preserve uncompacted structures and have oxygen isotopic ratios similar to that of sea-water. In contrast, concretions that formed later and/or at greater depths have lower carbonate content and lower 18O/16O ratios. Concretions in rapidly deposited sediments formed at shallow depths (<10 m), and those in sediments that accumulated slowly formed at greater depths. These differences agree with the fossil evidence. Siderite did not form until nearly all the dissolved sulphur had been reduced and precipitated as pyrite; the excess organic matter produced methane at about the same time.-H.R.B.
Publication type Article
Publication Subtype Journal Article
Title Siderite concretions: indicators of early diagenesis in the Gammon shale (Cretaceous).
Series title Journal of Sedimentary Petrology
Volume 52
Issue 3
Year Published 1982
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Sedimentary Petrology
First page 859
Last page 871
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