numerous radiocarbon dates, has divided the major deltaic lobes into 16 

 smaller units into which major flow of the Mississippi once occurred. The 

 Lafourche Delta, whose reworked sediments comprise Isles Dernieres, has been 

 subdivided into five smaller units by Frazier. Of these five units, the 

 fourth one, which was active approximately 1,200-400 years B.P., is respon- 

 sible for bringing most of the sediment to the Isles Dernieres area (Frazier 

 1967). This delta is the most extensive of the five and (like the other 

 lobes) was deposited by several distributaries. When the Mississippi changed 

 its course from the overly extended one of the Lafourche Delta in favor of a 

 shorter, more direct route to the sea, it began construction of the Plaque- 

 mines lobe to the east. Wave action and subsidence became the dominant forces 

 on the abandoned Lafourche Delta, and the gulf ward margin was reworked land- 

 ward. Isle Dernieres, an arcuate sandy beach consisting of reworked distrib- 

 utary front deposits, was formed as a result. Timbalier Island and Grand 

 Isle, located to the east of the Isles Dernieres, are parts of another delta 

 margin barrier complex formed from reworked sediments deposited by a slightly 

 younger one of the five Lafourche deltas. 



14. The Balize Delta of the present Mississippi is very different in 

 size, shape, and distributary characteristics from the earlier complexes. 

 These complexes had a roughly triangular outline, whereas the Balize Delta re- 

 sembles a bird's foot. The earlier deltas had a much larger area than the 

 modern Balize, which has an area of 768 km . The St. Bernard Delta comprised 

 an area of 7,680 km 2 , the Lafourche 5,888 km 2 , and the Teche 5,120 km 2 . The 

 major distributaries of the ancient deltas were more numerous, deeper, and 

 narrower, but the modern ones tend to be wide and shallow. The biggest 

 difference in the Balize Delta, as compared with the ancient deltas, is a 

 result of differences in the depth of water into which each prograded. The 

 Balize has developed near the edge of the continental shelf in water 

 originally reaching depths of greater than 90 m. Borings in the Lafourche and 

 St. Bernard complexes indicate that progradation occurred in water ranging 

 from 9 to 45 m deep (Kolb and Van Lopik 1966). 



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