Morphodynamics and Facies Architecture of Tidal Inlets and Tidal Deltas

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Abstract

Tidal inlets are highly dynamic systems marking positions along barrier coasts where dominant wave and longshore sand transport processes are juxtaposed with a tide-dominated regime in which onshore-offshore sand movement is manifested in the formation of flood- and ebb- tidal deltas. The morphodynamics of tidal inlets and distribution of their associated sand shoals are governed by the tidal prism, wave versus tidal energy, and the regional geological framework. Sand that is delivered to the inlet channel via longshore transport can be sequestered in the backbarrier, moved onto the ebb-tidal delta, or can bypass the inlet. Such bypassing is accomplished through wave and tidal processes and ultimately results in the landward migration and welding of large sand bar complexes to the downdrift shoreline. Tidal inlet-fill deposits typically exhibit a sharp basal contact with underlying units and consist of a fining-upward sequence in contrast to the generally coarsening-upward barrier lithosome. The preservation potential of inlet and associated tidal-delta deposits is high in regressive sequences, but relatively poor in transgressive systems due to the shallow nature of inlet-fill deposits compared to the base of the erosional wave- or tidal- ravinement surfaces. Exceptions occur in paleotidal inlet regions having large bay tidal prisms and deep inlet channels. Although tidal-inlet deposits have been reported in the rock record and may serve as important petroleum reservoirs, to date they are not readily recognized. High-resolution geophysical and sedimentological research of both active and relict inlets is providing a wealth of information necessary to improve the inlet facies models for ancient sedimentary sequences.