The potential of trace fossils as tidal indicators in bays and estuaries

Ichnological datasets have been used to infer the presence of tidal processes primarily through the identification of trace-fossil assemblages characteristic of brackish-water settings. However, this limited means of (ichnologically) identifying tidal settings is unsatisfying and the establishment of ichnological–tidal relationships for the purpose of discerning tidal depositional processes is desirable. We suggest that several types of ichnological data can be used to identify tidal influence: (1) ichnological response to rhythmic sedimentation; (2) the presence of tubular tidalites (i.e. biogenic structures infilled by tidally derived sediments); (3) the identification of anisotropic resource exploitation associated with food-rich slack-tide laminations; (4) the identification of tidal-flat deposits through bioturbation intensity and ichnological composition; (5) the recognition of brackish-water trace fossils; and potentially (6) system-scale ichnological distributions (which are presently poorly understood). As with tidal sedimentary structures, the inference of tidal processes from biogenic sedimentary structures should depend on identifying as many of the above characteristics as possible.