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2. Environmental studies of carboniferous sediments, Part I: Geochemical criteria for differentiating marine from freshwater shales;Degens;Am. Assoc. Pet. Geol. Bull.,1957
3. Environmental studies of carboniferous sediments, Part II: Application of geochemical criteria;Degens;Am. Assoc. Pet. Geol. Bull.,1958
4. Sedimentary organic matter and kerogen. Definition and quantitative importance of kerogen;Durand,1980