Cambrian wave-dominated tidal-flat deposits, central Wisconsin, USA

In central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open-coast, wave-dominated tidal flats. Mature, medium-grained quartz arenite is dominated by parallel-bedding with upper-flow regime parallel-lamination, deposited during high-energy storms that also produced three-dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths <= 2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain-drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel-bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal-flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low levees, point bars and cut-banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross-bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open-coast, wave-dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave-dominated and open-coast tidal flats documented to date appear to have been limited to mud-rich strata with 'classic' tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave-dominated tidal flats also can be recognized in the stratigraphic record.