result of glacial melting and regional subsidence of the coast (Kolb and 

 Van Lopik 1966; Numraedal 1983). Streams alluviated their entrenched valleys 

 to adjust to the rise in base level. When deposition could not keep pace with 

 the rise in sea level, the sandy deltas were forced farther upvalley deposit- 

 ing estuarine-marine sediments over coarse basal fluvial sediments as the 

 shoreline transgressed northward. As sea level continued to rise, both the 

 quantity and grain size of detritus supplied to the streams decreased, and the 

 site of sand deposition shifted rapidly upvalley leaving only fine sands, 

 silts, and clays for deltaic deposition (Kolb and Van Lopik 1966). 



11. Four to seven thousand years ago a standstill of sea level occurred 

 at approximately the present level. The Mississippi River began building a 

 series of lobate deltas in a gulfward direction displacing the gulf waters 

 that had extended up the Mississippi River alluvial valley to the latitude of 

 Baton Rouge, Louisiana (Kolb and Van Lopik 1966). The location of the 

 Mississippi River and its associated deltas shifted frequently during this 

 gulfward growth of land. 



12. The Mississippi River Deltaic Plain is composed of various active 

 and inactive deltaic complexes that extend 288 km across southwest Louisiana. 

 Several major deltaic complexes, which formed during the last 8,000 years, 

 have been identified in coastal Louisiana. These complexes reflect changes in 

 the course of the Mississippi River in recent time. From oldest to youngest, 

 the deltaic complexes are the Maringouin, Teche, St. Bernard, Lafourche, 

 Plaquemines, and the present Balize (Figure 5). The relative ages of these 

 complexes are well established, but the absolute ages are less accurate. Ages 

 were derived from Carbon 14 data and archeological evidence. 



13. The earliest deltaic lobes (the Maringouin and the Teche) were de- 

 posited mainly to the north and west of Isles Dernieres from approximately 

 8,000-3,500 years B.P. The Teche Delta complex once covered much of the area 

 now occupied by Isles Dernieres, and it has been proposed that reworked depos- 

 its of this complex may be present in the sediments of Isles Dernieres 

 (Peyronnin 1962). After progradation of the Teche system, the Mississippi 

 River shifted far to the east and started building the St. Bernard Delta. The 

 Chandeleur Islands are composed of reworked sediments of the St. Bernard Delta 

 complex. Approximately 2,000 years B.P., the St. Bernard Delta was abandoned, 

 and the Mississippi River was diverted westward where it started building the 

 Lafourche Delta lobe. Frazier (1967), using data from 500 borings and 



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