ABSTRACT

Cherty iron-formations (= ferriferous cherts) have sedimentary textures analogous to the sedimentary textures of limestones; it is possible to define textural rock types analogous to the micrites, intramicrites, oosparites, etc. of limestone classification. The close analogies between limestone textures and the textures of cherty iron formation permit paleogeographic interpretation of Precambrian iron formation by comparison with the textural facies of Recent limestones.

The Sokoman Iron Formation of the Central Labrador trough, Northeastern Quebec, Canada, is subdivided in five members on the basis of composition; these can be subdivided in sub-members distinguished by their textural properties.

Comparison of the distribution of facies types of the Sokoman Iron Formation with Recent limestone environments suggests deposition in two basically different environments: (1) A lagoonal platform probably composed of rapidly shifting banks of oolitic and intraclastic sand, of mud banks, and of small, lagoonal basins. (2) A basinal environment where relatively monotonous fine grained intraclastic sands, and rocks analogous to micrites were deposited. A narrow domain of oolite shoals separates both environments.

Traces of evaporites (length-slow chalcedony and pseudomorphs after gypsum) prove deposition of the Sokoman Iron Formation in a warm and comparatively dry climate.