Abstract

A combined study of regional stratigraphy, petrology, and paleocurrents was made of the Freda sandstone, Jacobsville sandstone, Bayfield group, Dresbach formation, and Franconia formation. Data pertaining to the location and nature of the source of the sediments were obtained primarily from petrology and directional sedimentary structures. Environmental reconstructions were based on patterns of lithologic variations, kinds of sedimentary structures, and heavy minerals.

This information indicates that the Northern Michigan highland extended through northern Wisconsin and northern Michigan and acted as a source of sediment from Late Keweenawan through Dresbachian time. The Freda formation accumulated in the Keweenawan basin, which was north of the Northern Michigan highland approximately in the present site of Lake Superior but extended considerably farther to the southwest. Deposition took place in a flood-plain and lacustrine environment. Prior to the deposition of the Jacobsville-Bayfield sediments, the Keweenawan sequence was deformed and eroded, but the Northern Michigan highland persisted as a positive area, and the shape and extent of the basin remained much the same. A lacustrine environment predominated in the central part of the basin, but much of the Jacobsville sandstone and Bayfield group undoubtedly represents fan deposits which merged northward into sediments of an alluvial plain. During Dresbachian time the Northern Michigan highland remained as a positive area, but shallow seas invaded the Lake Superior region from the northwest and central Wisconsin from the south. Most of the Dresbach sediments accumulated in a beach environment, but in southern Wisconsin an offshore neritic environment predominated. Prior to Franconian time there was a widespread regression of the seas, and most of the region was subjected to subaerial erosion. By Franconian time the Northern Michigan highland was reduced to a surface of low relief, and the seas re-advanced across the entire area from the southwest. An appreciable amount of the Franconia sediments accumulated in an offshore environment.

First Page Preview

First page PDF preview
You do not currently have access to this article.