The paleoenvironmental and paleoecological significance of the lacustrine Mermia ichnofacies: An archetypical subaqueous nonmarine trace fossil assemblage

Although nonmarine environments commonly are considered as diverse and varied as marine settings, only a single recurrent and archetypical ichnofacies, the Scoyenia ichnofacies, has been formally defined. However, recent research proposed the terrestrial Termitichnus ichnofacies as a subset of the Scoyenia ichnofacies. The Mermia ichnofacies is formally defined herein to include nonmarine, fully aquatic trace fossil suites characterized by the dominance of horizontal to subhorizontal grazing and feeding traces produced by mobile deposit feeders, the subordinate occurrence of locomotion traces, overall high to moderate ichnodiversity and abundance, and low specialized grazing patterns. The Mermia ichnofacies typifies unconsolidated, fine‐grained, permanent subaqueous substrates, and well‐oxygenated, low‐energy lake bottoms, periodically punctuated by episodic sedimentation. In addition, it is suggested to include in the Scoyenia ichnofacies, floodplain and transitional fluvio‐lacustrine trace fossil assemblages dominated by arthropod trackways, regardless of the presence of back‐filled meniscate burrows. In the nonmarine ichnofacies model proposed herein, the Scoyenia, Termitichnus, and Mermia ichnofacies are considered at the same hierarchical level. The Termitichnus ichnofacies is characteristic of terrestrial sediments, while the Scoyenia ichnofacies typifies transitional terrestrial/nonmarine aquatic environments, and the Mermia ichnofacies indicates nonmarine fully aquatic deposits. Various non‐marine ichnofacies remain unrecognized, potentially including ichnofaunas from dunes, fluvial channels, dry interdunes, and wave‐dominated lacustrine shorelines, as well as continental wood‐grounds, firmgrounds, and hardgrounds.

Key words:

• nonmarine ichnofacies
• paleoecology
• Mermia ichnofacies