Ebb-Tidal Delta Stratification and Its Relation to Tidal Inlet Processes: ABSTRACT

Abstract

Shallow, high resolution seismic reflection profiles at nine tidal inlets along the South Carolina coast have shown that ebb-tidal delta stratification is dominated by small to large-scale accretionary beds associated with channel cutting and infilling sequences. The deeper parts of the ebb-tidal delta (15 to 25 m) are comprised chiefly of shallow-landward and seaward-dipping beds (3 to 6°) and horizontal stratification. These beds represent initial sedimentation in large channel-fill sequences and original delta deposits. At intermediate depths (5 to 15 m) the stratification is dominated by large-scale (2 to 5 m in height) multidirectionally dipping accretionary beds (3 to 15°) that were formed owing to channel migration. Small channel cut and fill deposits are also prevalent at this depth. The upper delta is characterized by laterally continuous landward-dipping foresets formed by landward-migrating swash bars. Because of the depth of the ebb-tidal delta sediments (25 to 30 m) their preservation through a transgression appears likely. The development of this stratification is caused by a southerly migration of the inlet's main ebb channel through the ebb-tidal delta sediments. Eventually, the channel becomes hydraulically inefficient and a new channel is breached through a spillover lobe to the north. The abandoned channel is then filled with sediment that is derived from seawash sand shoals which flanked the old main ebb channel and with sand that is transported seaward in the new main ebb channel. The landward transport of sand which causes an infilling of the abandoned channel and a southerly migration of the main ebb channel is the result of accretion through bed-load sediment transport and landward-migrating swash bars. End_of_Article - Last_Page 707------------