Abstract

The Lower Cambrian "Fucoid Beds" of northwest Scotland are distinguished by an exceptionally high content of potash feldspar. In an attempt to explain the origin of potash, comprising as much as 10 percent of the dolomitic siltstones, a probable relationship between the feldspars and certain authigenic minerals within the succession has emerged. Various petrologic features of the rocks discredit a primary origin for the potash and suggest a post-depositional enrichment mechanism. It is hypothesized that the presence of illite in limestones overlying the "Fucoid Beds" favored dolomitization which, in turn, displaced potassium from the illite to be reprecipitated in the argillaceous "Fucoid Beds" as orthoclase. Dolomitization of illite would also displace excess silica which could simultaneously account for the cherts of the Durness Carbonates (Cambro-Ordovician). The hypothesis proposes only an internal redistribution of compositional ingredients contained within the original sediments to partly or wholly explain the authigenic processes of dolomitization, feldspathization, and silicification within these rocks.

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