The Petrology and Sedimentation of the Lower Proterozoic Barron Quartzite, Northwestern Wisconsin

Abstract

The Barron Quartzite of northwestern Wisconsin is a fine-grained, quartz-cemented, buff to red quartz arenite with minor interbedded argillite and a thin basal quartz-pebble conglomerate. The thickness of the Barron is at least 225 m (as shown by drill core) and may be greater than 400 m. Mafic dikes cut the Barron Quartzite but are as yet undated. The primary framework component of the Barron Quartzite is common quartz (75%). Polycrystalline quartz (grains with 2 to 5 component crystals), stretched polycrystalline quartz (composites of numerous suctured crystals), recrystallized polycrystalline quartz (grains made up of numerous. small. polygonal crystals) and vein quartz together make up approximately 16% of framework grains. Multicycle quartz grains (common quartz grains which have optically continuous overgrowths of quartz that have been abraded and surrounded by other overgrowths) are also present. Chert and iron-formation rock fragments occur but are rare. Feldspar is absent. Quartz cement, which occurs as optically continuous overgrowths on quartz grains, is common (approximately 9%) and hematite cement constitutes less than 1%. The heavy mineral suite is composed almost entirely of rounded zircon with minor rounded tourmaline and rutile, and minor magnetite. A possible depositional environment for the Barron Quartzite is a braided alluvial plain which was superseded by a marine shelf environment. Paleocurrent data are variable. Most localities show a unimodal pattern towards the south, indicating sediment transport form north to south. However, polymodal and bimodal-bipolar patterns are also present at some outcrops. A unimodal pattern probably indicates a fluvial depositional environment while a bimodal-bipolar pattern could suggest a tidally-influenced marine depositional environment. The Barron Quartzite is probably correlative with several of the other Precambrian quartzites in the Lake Superior region, including the Baraboo, Sioux, Flambeau, Waterloo, and McCaslin Quartzites. Of these, the Baraboo is the best dated, probably having been deposited between 1760 and 1630 Ma (Van Schmus. 1978; Van Schmus and Bickford. 1981).