Maringouin Delia 



As the ice on the continent began to melt about 15,000 years ago, sea level began to rise and 

 much of what is now south Louisiana was inundated by the gulf waters as far north as the latitude 

 of Baton Rouge. According to Frazier (1967) and Penland et al. (1987), there was a pause in the 

 rise of sea level about 7,000 years ago. When sea level was about 6 m below its present level, the 

 Mississippi River created a huge delta which extended as far south as Trinity, Tiger, and Ship 

 Shoals in the gulf. This delta was referred to as the Maringouin Delta by Frazier (1967) and 

 Penland et al. (1987) (Figure 5). The location of the upstream trunk channel of the Maringouin 

 Mississippi River is now buried and unknown. 



A post Maringouin Delta sea level rise resulted in the transgression of gulf waters over this old 

 delta. From about 5,500 to 3,500 years ago, the Mississippi River was flowing in the western part 

 of the valley and it developed the Teche Delta over a portion of the Maringouin Delta (Figure 

 6). 



St Bernard Delta 



There was a major change in the course of the Mississippi River about 3,500 years ago and the 

 Mississippi River built the St. Bernard Delta at New Orleans and east of New Orleans. As this 

 new delta continued to grow eastward, the older abandoned Teche Delta far to the west gradually 

 compacted and subsided and the gulf water encroached upon the Teche marshlands. Figure 7 

 shows the maximum development of the St. Bernard Delta and the transgression over the Teche 

 Delta. 



Lafourche Delta 



About 2,500 years ago a portion of the Mississippi River waters was diverted southward at 

 Donaldsonville and the river began to form the Lafourche Delta. As shown in Figure 8, the St. 

 Bernard Delta was gradually abandoned and transgressed by the gulf, and the Lafourche Delta 

 developed to its full extent. 



The Present Mississippi Delta 



As the Mississippi River established its present course and delta between the St. Bernard (Figure 

 5) and Lafourche Deltas, the Lafourche Delta was gradually abandoned (Figure 9). The older 

 Teche, St. Bernard, and Lafourche Deltas were constructed within the broad, relatively shallow 

 waters of the Continental Shelf. For the first time in its past 7,000-year history, the river is 

 presently building its delta at the outer margin of the Continental Shelf and sediments are slumping 

 into the deep waters of the gulf. Thus the seaward growth of the present delta has been extremely 

 slow. 



The Atchafalaya River Deltas 



Within historic time, part of the Mississippi River waters began to flow southward into a new 

 channel which developed at the junction of the Red River with the Mississippi, about 50 mi 

 northwest of Baton Rouge. Since that time this new Atchafalaya River has captured more of the 

 Mississippi waters each year. A report for the Mississippi River Commission by Fisk (1952) 

 predicted that by about 1980 the Atchafalaya River would have captured all of the Mississippi 

 waters. As a result of this report the U.S. Congress authorized the U.S. Corps of Engineers to 

 construct the Old River Control Structure (ORCS) to prevent this river diversion. 



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