Search

The trace fossil Ophiomorpha irregulaire Frey, Howard and Pryor, 1978, has been described chiefly from the Campanian (Upper Cretaceous) of the Book Cliffs of Carbon County, central Utah, U.S.A. Owing to the lack of type specimens and a well-defined type locality, a neotype and new paratypes are designated. Abundant material in the Spring Canyon Member of the Blackhawk Formation at Coal Creek Canyon, Book Cliffs, serves to supply a type locality and allows a more detailed description of the trace fossil than has been available hitherto, leading to an emended diagnosis. At the type locality, O. irregulaire is a shallow-tier trace fossil occurring in marine, delta-front or back-barrier, muddy, fine-grained sandstone. It probably represents the work of a crustacean deposit feeder. more...

The primary importance of trace fossils (biogenic sedimentary structures) to geologists is their great utility in reconstructing varous aspects of ancient depositional environments, including paleobathymetry, hydraulic regime during sedimentation, and [...] more...

The shallow-marine Carmel Formation (Middle Jurassic) in central Utah hosts low-diversity trace fossil assemblages, including Arenicolites, Chondrites, Gyrochorte, Lockeia, Planolites, Protovirgularia, Rosselia, Scalarituba, Skolithos, Taenidium, and Teichichnus. Non specialized ichnotaxa with a remarkably small burrow size dominate the assemblages. The amount of bioturbation is lower than expected in comparison with modern shallow-marine carbonate environments. These ichnological features also are significantly different from those of other Jurassic shallow-marine carbonates. The trace fossils represent an environmentally stressed benthic community in a marginal marine, restricted setting, with salinities above normal marine and with depletion of oxygen in pore waters. more...

Describes the trace fossil assemblages reflecting stressed environments in the middle Jurassic Carmel Formation in central Utah. Geologic setting; Stratigraphy and sedimentology; Systematic ichnology; Plug-shaped burrows; Trace fossil assemblages. more...

Although it is a pelagic sediment, fine-grained calcareous ooze may be mobilized prior to general lithification and redeposited as allochthonous units. Numerous occurrences of allochthonous chalk have been reported in recent years, having been recognized by large-scale bedding features seen in outcrop. Smaller-scale internal features, such as contorted laminae, and larger features, such as smeared burrows and imbricated flint nodules, attest to a significant amount of soft-sediment deformation and synsedimentary slumping in European chalk sections of Late Cretaceous age. Truly autochthonous chalks contain complex, tiered ichnofabrics and in some cases exhibits a diagenetic nodular fabric that is undisturbed by transport. In some situations, such as stagnant water conditions, autochthonous chalks may exhibit primary lamination, although this is very uncommon in European chalk sequences. Different types of redepositional processes produce an array of varied allochthonous fabrics. Glide and slump units, for example, contain internal deformational features produced during sliding. Ooze flow causes plastic deformation of chalk units, internally as well as externally. Resuspension and fluid flow of chalk sediment produces a deposit having a totally new fabric, such as a conglomerate composed of detrital chalk clasts. In this paper, typical macroscopic, sedimentary fabric types are illustrated, and the means of identifying them are discussed in terms of bioturbation features, in situ diagenetic nodules versus detrital clasts, physical deformation structures and development of flints. [ABSTRACT FROM AUTHOR] more...