Abstract
Analyses of Holocene sediments in over 80 vibracore, wash bore and auger drill holes from coastal North and South Carolina demonstrate sharply contrasting sedimentary sequences and processes of sedimentation between wave- and tide-dominated inlet-fill deposits. This variation in inlet sequences is primarily a function of the antipathetic relationship between wave height and tidal range in the study area. In addition to hydrographic regime, antecedent topography, sediment supply (i.e. sand versus mud) and lateral facies changes along dip are important factors in determining the sedimentologic nature of tidal inlet sequences. With a higher preservation potential for inlet deposits compared to other barrier island deposits, fining-upward sand- and/or mud-rich inlet sequences will dominate ancient clastic shorelines. Inlet channels rework the adjacent barrier island deposits, replacing characteristic coarsening-upward shoreface sequences with fining-upward tidal inlet sequences. Ephemeral, rapidly migrating wave-dominated inlets, filled by landward and longshore sediment transport, deposit a fining-upward sequence of: (1) inlet floor, a poorly-sorted, coarse shell and pebble basal lag; (2) active inlet-channel, planar and trough cross-bedded fine- to coarse-grained sand and shell; and (3) spit platform, planar cross-bedded and parallel laminated, well-sorted, fine-grained sand capping the sequence. Seawardmost wave-dominated inlet sequences are overlain by horizontally laminated overwash and/or cross-bedded and rooted eolian dune sands. Landward, inlet deposits are interbedded with fine-grained flood-tidal delta sands overlain by salt marsh. Ebb delta bar-bypassing at tide-dominated inlet mouths concentrates inlet deposits in the updrift portion of a barrier island. Seawardmost tide-dominated inlet sequences fine upward from basal trough and planar cross-bedded active inlet-channel sand and shell into a trough cross-bedded and rippled ebb-tidal delta sand. Coarsening upward foreshore sand and shell overlie abandoned-inlet deposits. Landward, the overlying ebb-tidal delta and foreshore sands interfinger with wavy- to lenticular-bedded silts and clays of the abandoned inlet-fill and bioturbated salt marsh which form an impermeable updip seal over the inlet channel. Isolation of these wave- or tidally influenced inlets by paleotopography confines inlet deposition to a small area, resulting in vertical stacking of abandoned inlet channels.
Published Version
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