Trace fossils from a carboniferous turbiditic lake: Implications for the recognition of additional nonmarine ichnofacies

Abstract

A high‐diversity ichnofauna from a Late Carboniferous turbiditic glacial lake at Cantera La Laja, northwest Argentina, includes Aulichnites cf. A. parkerensis, cf. Bergaueria isp., Circulichnis nton‐tanus, Cochlichnus anguineus, Gordia marina, Haplotichnus india‐naensis, Helminíhoidichnites tenuis, Helminthopsis tenuis, Mermia carickensis, Orchesteropus atavus, Palaeophycus tubularis, Planolites beverleyensis, Rusophycus isp., Treptichnus pollardi, Undichnia britannica, Vndichnia insolencia, string pits, and rhomboidal traces. Fifteen forms are present in fine to very fine sandstones and siltstones deposited by underflow currents, muddy turbidity currents, and suspension sedimentation in the deepest parts of the lake. Underflow and turbidity currents provided food and oxygen to deep‐lake settings, allowing the development of a rich biota. Alternation of fine‐grained laminae favored preservation of delicate and very small biogenic structures. The ichnofauna analyzed is remarkably different from the Sco‐yenia ichnofacies and to marine ichnofacies. The term "Mermia association” is suggested as the name of this distinctive ichnofauna. Diagnostic features of the association are: high diversity and abundance of trace fossils, absence of meniscate burrows, dominance of pascichnia, nonspecialized grazing patterns, and size reduction. Further studies in turbiditic lakes are required to test the universal validity of the Mermia association.