ABSTRACT

The Middle Precambrian Rove Formation as exposed in northeastern Minnesota is approximately 3200 feet thick, and consists of dark gray to black argillite overlain by interbedded argillaceous siltstone and sandstone. The sandstones appear to have been deposited by turbidity currents, for numerous laterally continuous sandstone beds are intercalated with argillite, and persistent sequences of structures occur within the sandstone beds indicating that each bed was deposited by a current of continually decreasing velocity. The orientation of directional structures, chiefly flutes and grooves, indicates that the currents flowed in a southeasterly direction perpendicular to the inferred shoreline.

Three lithologic units are recognized: (1) a lower argillite unit, 400 feet thick, (2) a transition unit of intercalated graywacke and silty argillite, 70 to 100 feet thick, and (3) a unit of graywacke and argillaceous siltstone, 2700 feet thick, having thin quartzitic beds in the upper 700 feet. Transition of rocks in the lower argillite to those in the thin-bedded graywacke records an increase in frequency of contribution of coarse detritus to the depositional basin.

The mineralogy of the rocks indicates that the source area was composed largely of granitic plutonic rocks and high grade metamorphic rocks, and to a lesser extent of low grade metamorphic rocks. The heavy minerals in the Rove Formation are similar in composition and relative proportion to those in the Lower Precambrian igneous rocks now exposed to the north of the Rove outcrop belt.