Chloroplast in Spirogyra From the Green River Formation of Wyoming

Abstract

A remarkable assemblage of micro-organisms, mostly algae, was found in a thin stratum of exceptionally rich oil shale from the Wilkins Peak Member of the Green River Formation of Eocene age. In this microflora is an almost perfectly preserved germling cell of Spirogyra, which still contains its spiral chloroplast. The cell is turgid and the dark-colored chloroplast appears to be suspended in a nearly colorless, transparent matrix. The preservation indicates that either the cell wall successfully resisted destructive attack by bacteria or saprophytic fungi or that, by chance, it actually was not attacked. The fact that this cell has retained its rounded, turgid form during the full compaction of the enclosing sediments implies that the cell wall was permeable enough so that virtually perfect hydrostatic balance was maintained between the fluids within and outside the cell. Certain other algal cells were flattened to a mere film and cracked radially. The organic ooze in which these organisms were preserved must have remained plastic during the whole process of compaction. This inference is supported by the fact that the thin varves in other nearby oil shale layers were distorted (locally) into sharply pointed peaks by the growth of shortite crystals. Such peaks would surely have lost their sharp crests had they formed before compaction had been completed.