Sedimentary petrology of the Sparagmites of the Rena district, S. Norway.

Abstract

Sediments of the Sparagmite group (Eocambrian\/latest Precambrian) have been mapped at a scale of 1:50 000 in the Rena district, 180 km north of Oslo. This district is located along the southern margin of the Sparagmite basin which is down-faulted in the crystalline Precambrian basement. The sediments are made up by a series of conglomeratic arkoses interlayered with shales and limestones. Toward the top of the Sparagmite group the arkoses grade into a quartzite which is overlain by a thin conglomeratic layer of granules which forms the base of fossiliferous Cambrian (Holmian series). The evidence for an Eocambrian glaciation existing in the Moelv tillite is discussed in the light of grain size and fabric analyses. Model analyses and flamephotometric determinations of sodium and potassium content in the sandstones show decreasing sodium\/potassium and plagioclase\/microcline ratio as the total feldspar content decreases towards the upper formation in the Sparagmite group. Spectrographic boron analyses suggest marine conditions during the deposition of the Sparagmite group, even if the analytical error of these analyses is rather high.