Trace Fossils of Problematic Origin: Assessing Silicified Trace Fossils From the Permian of Utah, U.S.A.

Abstract

Silicification is a diagenetic process that can affect the fidelity of trace fossil preservation. The combination of compaction and oversilicification associated with chert precipitation can alter the original fabric created by the trace producers. Sedimentary structures and trace fossils in mixed chert-carbonate systems are especially prone to these processes, leading to the preservation of a limited or biased ichno-assemblage and the omission of important paleoecologic detail. We summarize useful criteria for identifying chert-associated trace fossils and present a formal naming scheme. Using this nomenclature, we identified silicified trace fossils in the chert-rich Permian strata from northwestern Utah. An assemblage of burrows is present in outcrops of the Trapper Creek Formation, consisting of nodule-like growths of microcrystalline quartz in close association with bioturbated horizons. Thin section micro-textures of burrow fill lend additional support to the bioturbated origin of chert nodules. Silicified Thalassinoides fossils are present, as are chert nodules with a Rhizocorallium-like morphology.

The effect of siliceous sponge deposition on Permian paleocommunity structure

“…In these analyses, we make the assumption that more biogenic silica in the substrate, predominantly sponge spicules in this region of the Phosphoria Rock Complex (Murchey 2004), is equivalent to chert, whether it is nodular, bedded, or both. Chert is thought to alter and precipitate early on in diagenesis, exemplified by its association with both body and trace fossils (Bromley and Ekdale 1984; Maliva and Siever 1989; Wistort et al 2019). We draw the connection that biosiliceous deposition likely has an impact on substrate due to the abundance of spicular cherts in the Phosphoria Rock Complex, and the presence of chert is the best available data to track this.…”

Phosphorites, glass ramps and carbonate factories: The evolution of an epicontinental sea and a late Palaeozoic upwelling system (Phosphoria Rock Complex)

“…In the terminology of Wistort et al . (), the chert nodules in (C) are silicified trace fossils, those in (D) are trace‐like chert nodules, and (F) contains both (see description in Matheson & Frank, ). (G) A purple chert nodule in a dolomicritic host rock in the Tosi Member of 2‐16 ANR ( ANR ; ca 1255.5 m, 4119 ft).…”

“…C and D; Matheson & Frank, ). Both definitively silicified trace fossils and trace‐like chert nodules are present ( sensu Wistort et al., ). Nodules and host rock contain abundant monaxon siliceous sponge spicules (Fig.…”

“…In the terminology of Wistort et al . (), these nodules are both silicified trace fossils (based on spreiten) and trace‐like chert nodules (Matheson & Frank, ). Sedimentary structures include flat and microbial laminations as well as contorted laminations around (now silicified) enterolithic anhydrite.…”