The paleoenvironmental significance of the nearshore Curvolithus ichnofacies

Newly discovered Curvolithus-rich trace-fossil assemblages in fan-delta deposits of the Pennsylvanian Minturn Formation of Colorado are remarkably similar to several other Carboniferous deltaic ichnofaunas, as well as those from Jurassic fan-delta environments and other marginal-marine deposits with freshwater influence. The Minturn trace fossils comprise the type assemblage of the Curvolithus ichnofacies, dominated by infaunal locomotion-feeding activity in environments characterized by relatively rapid deposition of sandy sediment exceeding physical reworking. The ichnofacies also occurs in sandy, low-energy, open-shelf environments. Thus, the ichnofacies is a paleo-energy and paleo-depositional rate indicator, and we predict that its occurrence in strongly localized deltaic and nearshore sandy facies recurs throughout the Phanerozoic.