Possible Syneresis Origin of Valleys on the Floor of Lake Superior

Abstract

RELIEF features occur on the floor of Lake Superior in distinct zones which are related to bottom type and water depth1 (Fig. 1). Zone A occurs in sand and gravel deposits to about 54 m depth. Deeper, the generalized sequence of sediments is bedrock, glacial till and sand deposits, red clay, red varved clay, and brown clay2–4. In zone B, a network of intersecting linear grooves of width 5 to 75 m having relief of 2 to 5 m and lengths of greater than 2 km occur in a till and red clay bottom at about 54 to 165 m depth. The grooves were probably formed by scouring by icebergs during an earlier lake stage when the continental ice sheet formed a border of the lake. In zone C, below about 165 m, the bottom consists of lacustrine clays, and a series of narrow, V-shaped valleys occur extensively on echograms1. In this study, the valleys were examined by side-scan sonar, high resolution sub-bottom profiling, echosounding, and bottom sampling (Fig. 1).