t. Segment 20 . The lake floor in segment 20 is smooth to slightly 

 undulating with low ridges up to 1.5 meters high. The blue reflector 

 crops out throughout most of the area. Cores 81 to 93 were taken in 

 this segment. With one exception, these cores contain a predominance 

 of gray silt and clay covered by a thin sand veneer less than 0.6 meter 

 thick. Core 91 contains a 1.2-meter layer of fine to very fine sand 

 overlying the clay. A thin layer of gravel occurs at the top of cores 

 81 and 83, and a 0.3-meter (1 foot) layer of granules occurs at -1 meter 

 (-3 feet) in core 84. In general, prospects for obtaining sand or gravel 

 in quantity from this segment are poor. Some low, broad ridges which 

 occur in the northern part of the segment are probably the best sites 

 for further exploration. 



IV. SUMMARY 



The eastern shore of Lake Michigan between Manistee, Michigan, and 

 Bums Harbor, Indiana, was surveyed to locate offshore sand deposits 

 suitable for use in beach restoration and maintenance. Survey data con- 

 sist of seismic reflection profiles along 915 kilometers (569 miles) of 

 trackline and 93 cores up to 6.1 meters [20 feet) long. These data were 

 from water depths ranging from about 3.7 to 37.0 meters (12 to 120 feet). 



The predominant sediment types occurring in the study area are clean, 

 fine to coarse quartz sand and silty clay. Sand is the characteristic 

 surficial deposit. Silty clay is most characteristic of the shallow sub- 

 bottom deposits. Clay, gravel, and till-like mixtures of silt, sand, 

 pebbles, and cobbles occur locally. Shale occurs in one small area near 

 New Buffalo, Michigan. 



The best potential for offshore sand resources is in the area between 

 Whitehall and Saugatuck, Michigan. Localized deposits with good potential 

 occur in several places between Manistee and Whitehall, Michigan, and from 

 Saugatuck to 15 kilometers (9.3 miles) south of Benton Harbor, Michigan. 

 The area of lowest potential is that from Benton Harbor southward to Bums 

 Harbor, Indiana, where only a thin veneer of surficial sand overlies silt 

 and clay deposits. 



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