224
6 DEPOSITIONAL SYSTEMS
Fig. 6.34. Map showing the location of past, present and probable future lobes of the Mississippi delta. Six
lobes have been identified that predate the present one. The next, eighth, lobe may develop in Atchafalaya
Bay, unless the modern environment is grossly abused. (Based on Kolb and Van Lopik, 1966, and Shlemon
and Gagliano, 1972.)
These are in turn overlain by a suite of brackish and nonmarine fine-grained facies dissected by radiating distributary channel sands.
To the east of the present active mouth of the Mississippi lies the arcuate archipelago of the Chandeleur islands. These mark the edge of the abandoned lobe of the old
St Bernard delta. Once the sediment supply of a delta is cut off, it is extremely suscepFig. 6.35. Section of the Lafourche subdelta of the modern Mississippi, showing main locus of sand deposition as a sheet at the delta front. This is gradually buried beneath a prograding sheet of delta-plain muds and
peats deposited in interdistributary bays and swamps, with minor distributary channel sand bodies. (After
Gould, 1970. Courtesy of the Society for Sedimentary Geology.)
6 DEPOSITIONAL SYSTEMS
Fig. 6.34. Map showing the location of past, present and probable future lobes of the Mississippi delta. Six
lobes have been identified that predate the present one. The next, eighth, lobe may develop in Atchafalaya
Bay, unless the modern environment is grossly abused. (Based on Kolb and Van Lopik, 1966, and Shlemon
and Gagliano, 1972.)
These are in turn overlain by a suite of brackish and nonmarine fine-grained facies dissected by radiating distributary channel sands.
To the east of the present active mouth of the Mississippi lies the arcuate archipelago of the Chandeleur islands. These mark the edge of the abandoned lobe of the old
St Bernard delta. Once the sediment supply of a delta is cut off, it is extremely suscepFig. 6.35. Section of the Lafourche subdelta of the modern Mississippi, showing main locus of sand deposition as a sheet at the delta front. This is gradually buried beneath a prograding sheet of delta-plain muds and
peats deposited in interdistributary bays and swamps, with minor distributary channel sand bodies. (After
Gould, 1970. Courtesy of the Society for Sedimentary Geology.)