Abstract: 

Distributary-mouth bars are important morphological units of deltas which develop under a wide range of wave, tidal, and riverine conditions, and are known to form highly productive subsurface oil and gas reservoirs. This paper extends previous work on purely fluvial mouth bars, to mixed systems where tides are also present. Under these conditions mouth bars can display alternate layers of mud and sand that can ultimately determine their vertical permeability. Herein we propose an analytical, process-based model to explain characteristics of tidal bedding and quantify their extent in mouth bars. Findings from our analytical model are compared with results from the numerical model Delft3D. From landward to seaward and in the absence of tides, our analysis shows that a sand-dominated zone is followed by a depositional environment made of sand and mud mixtures, and finally by mud-dominated areas. With increasing tidal amplitude, the sand–mud mixture zone is gradually replaced by a lamination zone characterized by alternate tidal bedding. Bedding characteristics in mouth bars are defined using the extension of the lamination area and the difference in mud content between coarse and fine sediment layers. Both quantities tend to increase with increasing tidal amplitude. The lamination zone grows while the difference in mud content decreases for small ratios of mud to sand settling velocity and mud to sand concentration. Bottom friction strongly affects tidal bedding by reducing the length of the zone where lamination occurs and increasing differences in mud content between successive layers.

You do not currently have access to this article.