pluralization of the name. The islands consist of marsh areas along most of 

 the mainland side and sand beaches on the Gulf of Mexico side. These beaches 

 average approximately 30 m in width and are rarely backed by dunes. Peyronnin 

 (1962) and Penland and Suter (1983) have conducted extensive coring projects 

 on Isles Dernieres and found that the beach-ridge deposits range from 1.8 to 

 6 m in thickness and are underlain predominantly by bay deposits (Figure 2). 

 The backshore slopes down into low marshy areas or open water. A large bay 

 (Lake Pelto) is situated between the mainland and Isles Dernieres. This bay 

 has increased in size dramatically due to increased erosion and subsidence of 

 the mainland marshes flanking the island (Figure 3). 



3. The origin of Isles Dernieres is attributed to reworking of the 

 abondoned Lafourche Delta and subsequent barrier spit accretion on both ends 

 of the island. As the deltaic headland is attacked by waves, finer sediments 

 are winnowed out and carried offshore while coarser sediments remain behind. 

 These coarser sediments become reworked landward and laterally, creating a 

 barrier beach. Mechanical analysis of the sediments revealed that the beaches 



ISLES DERNIERES 



x&* 



WEST 



j^ro^ •• jf *t c°r: v/ ^. 



EAST 



20 30 



DISTANCE, KM 



REGRESSIVE FACIES TRANSGRESSIVE FACIES 



DISTRIBUTARY 

 DELTA FRONT-PRODELTA 

 |» *| BEACH RIDGE 



| J [ BARRIER 

 fcyj BAY- LAGOON 

 • CORE LOCATION 



Figure 2. Stratigraphic strike section depicting the 

 facies relationships through the Isles Dernieres 

 (after Penland and Suter 1983) 



