Abstract

An anthracitic carbonaceous sedimentary rock interbedded in the upper Huronian, Michigamme shales of the Iron River District, Michigan, has been subjected to intensive petrographic and chemical analysis as well as x-ray diffraction study. Field studies were aided by small-scale stripping and trenching operations. The coal occurs as lenticular bodies concordantly bedded with the Michigamme black shale. Similar relations between anthracitic coal and black shale have been observed in drill cores taken at a depth of 1000 feet several miles distant. The associated black shales exhibit numerous graphitic elliptical bodies of varying size but relatively constant form. These are interpreted as being of organic origin. Numerous small elliptical structures may also be observed in flame-etched polished surfaces of the anthracitic coal. X-ray diffraction patterns demonstrate that the coally sedimentary rock is partially graphitized, but less so than that of Rhode Island meta-anthracite of Pennsylvanian age. Use of various extractive and chromatographic techniques demonstrates the presence of strongly pigmented organic compounds. The organic extractives show strong fluroescence in ultraviolet light, solubility in both acid and base solutions, color change with pH change, relatively featureless absorption spectra in the visible and ultraviolet light, and high thermal stability. Oxidative treatment increases the yield of organic extractives. Concatenation of the evidence on the origin and composition of the Michigamme anthracitic carbon suggests probable derivation from algal remains. The sedimentary rock is, hence, of much interest in connection with the problem of the antiquity of Precambrian life.

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