Siliciclastic Back-Barrier Tidal Flats

Abstract

Back-barrier tidal flats occur along micro- to mesotidal coasts landward of barrier islands and in the shelter of coastal sand spits and bars. Tidal flats are generally flood dominated, the grain size progressively decreasing shoreward. The sediment can be divided into sand, slightly muddy sand, muddy sand, sandy mud, slightly sandy mud, and mud. The mud fraction consists of non-cohesive sortable silt and cohesive flocs and aggregates. Important physical and biological surface structures include wave- and current-generated ripples, ladderback ripples, washed out ripples and other late-stage emergence runoff features, shell pavements, fluid mud sheets, tool marks, crawling, feeding and resting traces of intertidal organisms, as well as the feeding traces and tracks of birds. Internal sedimentary structures range from rare dune cross-bedding to ubiquitous ripple cross-bedding in sand, through flaser, wavy and lenticular bedding in mixed sediment, and homogenous or laminated mud toward the high-water line. Bioturbation may be intense, but the preservation potential depends on the frequency and depth of reworking. The transition from land to sea is typically marked by laminated versicolored microbial mats. The interaction between sea-level rise and sediment supply defines the sediment budget and hence the stratigraphy. Prograding, aggrading or transgressive systems are easily distinguished by their stratigraphic architecture.