361 WELLS, J. T. 1987. "Effects of Sea-Level Rise on Deltaic Sedimenta- 

 tion in South-Central Louisiana," Nummedal , D., Pilkey, 0. H., and Howard, 

 J. D., eds . , Sea-Level Fluctuations and Coastal Evolution . Special Publication 

 No. 41, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, 

 pp 157-166. 



The birth of two new deltas in Atchafalaya Bay of south- central 

 Louisiana has provided scientists with a unique opportunity to observe and 

 measure processes of delta growth in their incipient stages. These regressive 

 deposits, localized along a transgressive shoreline that is characterized by 

 low- lying marsh and eroding barrier island, have developed in a setting in 

 which compactional subsidence accounts for approximately 90% of the relative 

 rise in sea- level. Unlike previous Holocene deltas of the Mississippi River 

 and its distributaries, however, the deltas in Atchafalaya Bay may soon be 

 growing under conditions of eustatic sea- level rise that is so rapid it will 

 exceed rates of subsidence (1-2 cm/year). 



Extrapolation of delta growth under three sea- level rise scenarios 

 (subsidence only 1 cm/year, and 2 cm/year) indicates that as rates of eustatic 

 sea- level rise approach or exceed rates of subsidence in south Louisiana, the 

 subaerial deltas in Atchafalaya Bay will continue to grow but at slower rates. 

 Even at the extreme rate of sea-level rise scenarios (subsidence only, 1 

 cm/year, and 2 cm/year) indicates that as rates of eustatic sea- level rise 

 approach or exceed rates of subsidence in south Louisiana, the subaerial 

 deltas in Atchafalaya Bay will continue to grow but at slower rates. Even at 

 the extreme rate of sea- level rise of 2 cm/year, sediments will accumulate 

 subaerially for another 80-100 years. Perhaps contrary to expectations, the 

 slower a delta grows, because of rising sea-level, the more likely it is to be 

 limited by inefficiency of channels and an inability to deliver sediments to 

 its distal areas than it is to be limited by receiving basin area. Thus, a 

 decrease in subaerial growth rate is reflected by a decrease in delta size. 



In addition to producing smaller deltas, high rates of sea-level rise 

 will affect sedimentation processes by leading to thicker sand bodies and 

 deposition of sands farther upstream. High-energy environments of deposition, 

 such as natural levees which grow primarily during spring floods, will keep 

 pace with sea-level rise. Low-energy environments of deposition, such as back 

 bar algal flats, will remain or become subaqueous as waters rise faster than 

 sediments are introduced. Furthermore, high rates of sea- level rise will 

 delay the extension of deltaic sediments to the continental shelf. This, in 

 turn, will slow the growth of downdrift mudflats to the west. Accelerated 

 growth of downdrift sediments will occur when Atchafalaya Bay becomes 

 sediment-filled (2035-2085 a.d.), thus allowing a greater volume of sediments 

 to enter the dynamic shelf region seaward of the bay. (Author). 



362 WEYER, E. M. 1979. "Pole Movement and Sea-Levels," Nature . Vol 273, 

 pp 18-21. 



If the centrifugal force generated by a surface load caused the Pole to 

 shift, sea-levels would fluctuate differentially around the world. Applica- 

 tion of the 'hydrodynamic ' formula to seemingly incongruous shoreline samples 

 dated 14,700 to 28,000 BP suggests rhythmic polar oscillations on a 5,600 year 

 cycle, synchronized with two glacial episodes. (Author). 



166 



