Influence of Island Migration on Barrier-Island Sedimentation

Barrier islands migrate along some coastal areas in the direction of dominant sediment transport. At the forward end of the island deposition occurs on the margin of the channel where the environment strongly influences the characteristics of barrier-island deposits. The depth of the channel, for example, exceeds two-to-three times that of other environments associated with barrier deposits. Moving along the coast, the channel erodes and reworks the deposits of other environments. The reworked area extends landward and seaward of the inlet and is several miles wide. The depth of reworking and the subsequent deposition preclude further modification by other agencies of the barrier-island environment. The erosion that accompanies transgression and regression may remove the upper level of barrier deposits, leaving modified channel sediments for interpretation and identification. Sedimentary modifications produced by island migration include textural changes, gross shape of the deposit, and steepening and reorientation of stratification. Recognition of the reorientation of stratification is particularly important in paleocurrent analysis. Modified channel sediments inter-finger seaward with shallow neritic deposits and landward with lagoonal salt-marsh sediments. Although the duration of the Holocene high stand of the sea was too short to permit major migration-modification of Holocene islands, there was probably enough time for the extensive reworking of many ancient deposits. Studies on channel sediments and on the extent of island migration can provide information on the environment during the deposition of coastal sediments.