Table 3. Summary of Quaternary geologic events (dates 

 from Newman, 1977) . 



Age (yr) 



Event 



12,300 Co present 



As sea Level rose, Long Island Sound became a tidal 

 estuary and deposition of organic muds and sandy silts 

 occurred. Sources of these sediments were and continue 

 to be coastal erosion of glacial deposits, rivers drain- 

 ing glacial terrain, and sediment influx from Block. 

 Island Sound and the adjacent Continental Shelf. 



13,400 



Short-term readvance or slowing of retreat of the 

 glaciers that were part of the Port Huron scade. This 

 led to deposition of the several discontinuous terminal 

 moraine segments (Elmhurst, Madison, Old Saybrook, Six 

 Mile, Ledyard, and Middletown) close to the Connecticut 

 coast on Long Island Sound. 



15,000 to 13,400 



Damming by the Ronkonkoma and Harbor Hill Moraines 

 backed up freshwater and created Lake Flushing that 

 covered much of Long Island and Block Island Sounds. 

 Very fine grained silt and clay were deposited as 

 seasonal varves filling in and covering the high-relief 

 bedrock surface and glacial deposits. 



21,000 to 15,000 



Late Wisconsin advance of the glacier resulted in depo- 

 sition of the Harbor Hill Moraine consisting of till and 

 stratified kame and outwash deposits. Existing river 

 valleys were deepened and widened. 



7T 



-41*10' — I — — I — J — — 



CONNECTICUT 00 »« Al J 



+ 



Contours in Feel 



I 2 3 4 5 km 



Figure 10. Flint and Gebert (1976) have shown that the Old Saybrook. Moraine is present 

 along the Connecticut coast from Niantic Bay to Hammonasset Point and then 

 extends southwest into the Sound. Results of this study reveal that Six Mile 

 Reef is a moraine segment and Long Sand shoal originated as an outwash deposit 

 that has been lengthened to the west by estuarine processes. 



28 



