The <i>Teichichnus</i> Ichnofacies: Its neoichnological basis and identification in the rock record

Abstract Research on the ichnology of brackish‐water environments began in the 1930s and has led to the identification of predictable infaunal patterns. Brackish‐water deposits characteristically display low‐diversity tracefossil assemblages consisting of both vertical and horizontal structures. These salinity‐reduced ecosystems are dominated by opportunistic euryhaline‐tolerant species. Osmoregulation‐related selective pressures lead to decreased diversity and an abundance of infaunal organisms. In environments with fluctuating or low salinity, fauna adopt r‐selected strategies and are characterized by rapid colonization dynamics, high population densities, elevated mortality rates and low‐diversity assemblages. Tides in brackish‐water settings contribute a plentiful food supply with tidal currents transporting marine‐sourced and terrestrially sourced organic matter that settles on the sediment–water interface during slack‐water periods. This increased food availability favours trophic generalists using various feeding strategies to exploit both intrastratal and surficial food resources. The ichnological characteristics of modern and ancient brackish‐water strata are used to propose the Teichichnus Ichnofacies; they are temporally and spatially recurrent and reflect the biology of brackish‐water settings. The Teichichnus Ichnofacies is recognized by reduced trace‐fossil diversity, smaller trace sizes, dominance of structures reflecting trophic generalist behaviours, sporadic distributions of ichnofossils, locally high bioturbation intensities and opportunistic colonization. This ichnofacies is characterized by trace fossils interpreted to be associated with surface deposit feeding, intrastratal deposit feeding and subordinate filter feeding.