of the moraine (Fig. 10) comprises the ridge and the flat elevated platform' 

 immediately west of Presque Isle, but there is some evidence that minor 

 glacial deposits or erosional remnants are present several kilometers 

 east of Presque Isle and also northwest of the shore of Dans Beach near 

 the Ohio border. All these glacial deposits .ppear to be related to the 

 same glacial event, which is likely the Port Huron advance that has been 

 age-dated by several investigators at about 13,000 years before present (B.P.). 



Adjacent to the ridge is a gray-brown firm clay unit with scattered rounded 

 pebbles at the lake floor; several cores and seismic profiles show that it 

 has considerable thickness. The unit is most likely lacustrine in origin and 

 was deposited in an earlier Lake Erie formed when the moraine dammed and backed 

 up normal melt-water drainage. The clay unit's firm nature suggests that it is 

 slightly overconsolidated, possibly the result of subaerial exposure when the 

 ridge was breached and the lake level dropped. Erosion of the clay unit to the 

 west of the ridge has left a lag deposit veneer of coarse-grained sediment in 

 places that form isolated ridges with relief of several meters. Some of these 

 small ridges, which are semiparallel to the main ridge, are asymmetric suggest- 

 ing that they may be active and maintained by bottom currents caused by wind 

 shear or barometric seiche action. 



c. Beach and Dune Deposits . Following retreat of the glacier that depos- 

 ited the Long Point-Erie Moraine, the outlet at Niagara Falls rebounded in i 

 elevation and present-day Lake Erie was formed. 



The radiocarbon-l4 dates of wood fragments contained in cores 4, 18, 23, 

 and 28 (Table 2, Fig. 11) show that as early as about 11,000 years ago lake 

 levels were still at least 22 meters below the present levels and remained there 

 until at least 6,870 ± 150years B.P. As lake levels gradually rose during this 

 time the ridge and Presque Isle platform were high-energy coastal areas sub- 

 jected to active littoral processes. The glacial tills were washed and sorted, 

 and much of the fine-grained sediment was carried offshore and ultimately depos- 

 ited in deeper parts of the basin. The beach and dune deposits that mantle the 

 ridge and platform were derived directly from erosion of local glacial debris. 

 The stabilization of lake levels over the past several thousand years has 

 resulted in the sand being eroded from the ridge-platform and transported 

 eastward to form Presque Isle Peninsula. 



d. Modern Soft Mud . Several of the cores in deeper water adjacent to the 

 Presque Isle platform and ridge contain gray, very soft mud with high water 

 content and very low shear strength. Figure 5 shows that mud is especially 

 common east of Presque Isle, and also present in troughs on the platform 

 northwest of Presque Isle. Fine-grained material is being deposited at the 

 present time throughout much of the Lake Erie basin except for relatively 

 high-energy areas, such as along the coast or on elevated areas. The pre- 

 dominance of muddy sediment in the samples east of Presque Isle and the lack 

 of sand suggest that sand from the eastern end of Presque Isle is not being 

 transported eastward off the platform in any significant volume. 



2. Potential Sand and Gravel Deposits . 



Analyses of the seismic and core data show that two separate areas, the 

 ridge-platform moraine complex and the moraine ridge segment off Dans Beach, 

 contain large quantities of clean (small percentages of silt and clay). 



19 



